fix timestampable use of datetimeclass #1584

Job	Run time
code-style-and-static-analysis	1m 18s
Test Suite (7.4, sqlite, 5-min)	57s
Test Suite (7.4, sqlite, 5-max)	56s
Test Suite (7.4, mysql, 5-min)	1m 16s
Test Suite (7.4, mysql, 5-max)	1m 7s
Test Suite (7.4, pgsql, 5-min)	1m 11s
Test Suite (7.4, pgsql, 5-max)	1m 8s
Test Suite (7.4, agnostic, 5-min)	34s
Test Suite (7.4, agnostic, 5-max)	39s
Test Suite (8.2, sqlite, 5-min)	45s
Test Suite (8.2, sqlite, 5-max)	1m 0s
Test Suite (8.2, sqlite, 6-min)	55s
Test Suite (8.2, sqlite, 6-max)	42s
Test Suite (8.2, sqlite, 7-min)	58s
Test Suite (8.2, sqlite, 7-max)	52s
Test Suite (8.2, mysql, 5-min)	36s
Test Suite (8.2, mysql, 5-max)	33s
Test Suite (8.2, mysql, 6-min)	32s
Test Suite (8.2, mysql, 6-max)	31s
Test Suite (8.2, mysql, 7-min)	39s
Test Suite (8.2, mysql, 7-max)	33s
Test Suite (8.2, pgsql, 5-min)	1m 6s
Test Suite (8.2, pgsql, 5-max)	1m 6s
Test Suite (8.2, pgsql, 6-min)	1m 6s
Test Suite (8.2, pgsql, 6-max)	1m 7s
Test Suite (8.2, pgsql, 7-min)	1m 9s
Test Suite (8.2, pgsql, 7-max)	1m 15s
Test Suite (8.2, agnostic, 5-min)	25s
Test Suite (8.2, agnostic, 5-max)	23s
Test Suite (8.2, agnostic, 6-min)	22s
Test Suite (8.2, agnostic, 6-max)	26s
Test Suite (8.2, agnostic, 7-min)	24s
Test Suite (8.2, agnostic, 7-max)	26s
	26m 57s

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