What is "Elapsed" measuring in ColumnStore query plan

I have a query that reports an execution time of 6.826 sec. I was expecting the sum of the elapsed to be something less that the total execution time. The query plan shows BPS step of 6.095 and TAS 6.059.

Here's the query and results...

-- version=10.2.10-MariaDB-log         
-- version_comment=Columnstore 1.1.2-1   
RESET QUERY CACHE;
SELECT calFlushCache();
SELECT calSetTrace(1);
 
SELECT DAY(timestamp_),SUM(numeric_val), AVG(numeric_val) 
    FROM cs1
    WHERE timestamp_ >= '2017-09-01 00:00:00' AND timestamp_ < '2017-10-01 00:00:00'
      AND id IN (228091,228231,228233,227867,228216,228241,226331,227950,228254,227953,228156,228160,228164,211566,227827,227875,227886,227892,211111,211576,224213,227908,224293,211117,227919,224232,227850,227925,226290,227853,227261,210432,210443,210446,210477,211314,227391,211634,227396,226377,227485,211630,227385,211532,226814,211542,226825,210063,210081,210092,210287,210289,210252,210303,210326,210263,210339,226979,226984,210362,227019,227045,227055,227062,210376,227132,227133,227142,227169,210403,227240,209894,209895,209907,209896,209931,209946,209948,207054,209975,210009,210021,210023,210020,207181,207243,206201,206332,209821,209824,209839,209772,209773,209777,209851,209855,206559,209862,209870,206575,209878,185470,185475,185027,185044,185045,185052,185059,185041,185072,184223,185085,184339,185128,184369,184341,185108,184355,184372,185185,184860,184139,184145,184880,184146,184162,184934,184165,184941,184943,184894,184174,184960,184169,184930,184975,184210,184915,184987,184998,185013,381854,376280,413343,342336,412480,327684,412489,414657,414658,416331,318587,414660,414603,319965,319973,319975,412457,412464,342329,342330,413163,381783,412652,413696,412096,412661,413707,413710,413048,342333,412477,381805,381821,381825,381826,320421,342318,413007,413009,412411,412412,376236,412418,376240,376242,413338,414025,412443,412627,413018,412445,376266,412447,412449,413024,323373,325478,325163,326013,325752,323387,319958,321642,321643,320948,414942,328239,327041,412296,335091,412303,411961,335096,411965,334263,317730,321466,320413,321295,320940,319779,322531,325472,325473,325741,325742,334396,327907,334565,317724,321293,411940,411942,333900,327567,334594,412284,334418,333918,334432,333935,334444,229724,229727,230088,230470,230784,230785,230119,229657,230507,229853,229735,230624,230625,230633,230637,229647,230078,230457,230658,230794,230797,229716,230108,230501,230680,230681,229479,229530,229558,230035,230401,230595,229677,230050,230424,230425,229693,230602,230604,230610,229620,230618,229301,229295,228569,229313,229315,229359,229365,229386,229338,229393,229395,229428,229442,229473,228899,228883,229227,228488,229069,228913,228920,228516,228926,229285,229097,229106,229082,228508,229166,229013,228853,229033,228753,228430,228864,229219,229220,229229,228455,228358,228676,228631,228637,228807,229128,228827,228982,228708,228987,228997,228845,228171,228289,227963,228315,228769,228777,228181,228786,228184,228185,228616,228621,228190,228328,228813,228656,228350,228959,224241,228101,228104,426454,425833,425836,413952,414530,424627,414534,424633,413866,413971,413972,413973,413979,327692,381675,376161,412051,334521,381690,381695,414229,412225,412745,413313,412231,412233,414501,414863,414512,412748,413942,412755,413325,414518,413949,415149,415453,323391,426539,412910,413749,334724,412821,425661,416180,425785,415892,415894,412915,412916,412918,414494,413677,413838,413478,335201,414195,412203,325623,414201,413492,414207,414208,414209,414215,414483,414481,342351,414075,325963,326022,324753,319794,424584,415146,318590,317417,318722,318604,318605,317939,317742,413661,413907,413914,413465,414835,413921,413477,412593,320294,320638,376452,376456,320152,319995,320648,415450,415787,426952,415140,206051,207347,206095,207411,206119,206129,206135,206138,206224,206230,206234,206239,206283,206262,206361,206268,206287,205903,204852,204863,204884,204886,204891,204893,204895,204905,204922,204923,205919,205932,205067,205987,205991,205992,206007,206032,205729,205735,205747,204759,205765,205764,204766,205772,205774,205782,204793,205797,204803,205867,204826,204264,204298,204342,204469,205653,204333,204334,204539,204682,204728,205688,205696,205715,186694,203811,204024,203933,203935,204055,203955,204132,204139,204163,204175,204183,187187,186497,186500,186505,187532,186529,187547,186619,187665,186662,187684,186689,185872,185875,186882,186888,186901,186947,185967,185973,186956,186280,186282,186981,186986,186990,187040,187045,185756,185758,185760,185689,185691,185766,185697,185769,185776,184641,184643,186771,186786,184677,186796,186828,186833,186834,186861,184547,184558,184541,185238,185249,185254,185269,185284,185318,185319,185721,185727,185603,185204,184401,184405,184419,184431,184436,184448,184472,184473,184455,184450,184457,184492,184494,184534,185355,185359,185452,185454,369745,386083,369047,376014,408619,392018,409158,392020,371823,410732,371827,387721,386370,369154,390888,387707,380161,378386,382047,382048,384200,386588,386593,384936,379230,389609,368007,371783,367934,371785,371790,410710,371793,387862,378058,391020,410876,371799,371803,371805,386068,385516,385518,386339,367927,385610,375919,384736,385617,378379,384193,372456,384194,375993,379359,409657,385510,415122,424790,415126,424579,415133,424911,424799,415129,424914,328605,415852,426520,424896,414790,424564,415249,416146,427011,415439,415257,415867,426521,415262,415263,415264,415871,415873,426939,426523,424573,424575,415890,415845,414738,424880,424885,415209,414752,426920,415103,416388,414763,415226,426513,415231,415108,414777,414778,414779,415084,415389,425615,426887,415175,415391,414717,426894,415409,415411,426903,424553,415181,415190,416111,424877,415289,415166,426968,426971,426546,424618,424394,425667,424621,424395,426554,425795,424410,415314,425798,412953,412954,415737,416378,415746,424343,414098,381882,381903,413388,326880,376349,413210,412681,414430,326201,320442,320444,425342,415912,415292,416192,414088,412842,342360,413528,413534,413525,414093,343060,412849,376313,413383,376334,412137,412139,413196,412537,413539,376316,413765,413076,425598,425744,425604,326198,415080,427548,324778,326038,416447,424932,427047,427048,416372,414082,414990,414549,415906,425344,334729,334730,381863,413178,413180,320433,415282,320320,320321,320437,424635,424303,425789,326739,325757,326744,326368,324935,424610,427042,426643,413349,416366,425391,424532,424864,424536,424698,424699,415807,424709,415367,415805,415072,424856,320170,424600,428564,427120,428583,320652,320308,425382,425722,414607,415060,416345,381705,381700,381717,376175,342992,342293,412372,376188,334536,335216,327717,334692,341030,380383,380387,391224,393412,393415,378189,380323,408010,411552,410845,393315,393318,388598,411435,388980,388594,385447,379487,371580,371587,383788,391953,388983,383750,385136,385139,383763,391959,322976,370657,393312,322972,367863,377385,409309,411711,411713,385669,340995,390659,411226,411734,341011,341015,383560,380212,376563,381209,380215,380219,381212,410765,391092,341165,371570,377379,391710,391942,391083,393305,391094,391097,391098,368906,382540,367173,386240,386241,322885,391734,370515,387510,370798,368715,372518,376550,383534,322970,372515,381198,380203,391926,371653,383270,393138,370793,383516,371890,409188,391066,407948,371704,386133,376524,381167,380194,385850,367415,367417,380189,385561,385563,367853,367855,379445,391699,384618,391703,372120,372129,386417,391193,387409,386403,376078,376487,376490,376493,376090,376108,376516,408644,370789,390342,369178,387757,387764,391209,387493,367950)
      GROUP BY DAY(timestamp_)
      ORDER BY DAY(timestamp_)
;

SELECT calGetTrace(); 
/*
Desc Mode Table           TableOID ReferencedColumns                          PIO    LIO    PBE     Elapsed Rows 
BPS  PM   cs1             3161     (numeric_val,id,timestamp_)                321404 119576 1347584 6.095   6652 
TAS  UM   -               -        -                                          -      -      -       6.059   30   
*/
SELECT calGetStats();
/*
Query Stats: MaxMemPct-0; NumTempFiles-0; TempFileSpace-0B; ApproxPhyI/O-321404; CacheI/O-119576; BlocksTouched-119960; PartitionBlocksEliminated-1347584; MsgBytesIn-3MB; MsgBytesOut-41KB; Mode-Distributed
Execution Time : 6.826 sec
*/