fix timestampable use of datetimeclass #1583

Job	Run time
code-style-and-static-analysis	1m 12s
Test Suite (7.4, sqlite, 5-min)	53s
Test Suite (7.4, sqlite, 5-max)	1m 19s
Test Suite (7.4, mysql, 5-min)	1m 15s
Test Suite (7.4, mysql, 5-max)	1m 45s
Test Suite (7.4, pgsql, 5-min)	1m 12s
Test Suite (7.4, pgsql, 5-max)	1m 48s
Test Suite (7.4, agnostic, 5-min)	35s
Test Suite (7.4, agnostic, 5-max)	53s
Test Suite (8.2, sqlite, 5-min)	50s
Test Suite (8.2, sqlite, 5-max)	49s
Test Suite (8.2, sqlite, 6-min)	57s
Test Suite (8.2, sqlite, 6-max)	50s
Test Suite (8.2, sqlite, 7-min)	48s
Test Suite (8.2, sqlite, 7-max)	49s
Test Suite (8.2, mysql, 5-min)	31s
Test Suite (8.2, mysql, 5-max)	56s
Test Suite (8.2, mysql, 6-min)	52s
Test Suite (8.2, mysql, 6-max)	49s
Test Suite (8.2, mysql, 7-min)	40s
Test Suite (8.2, mysql, 7-max)	50s
Test Suite (8.2, pgsql, 5-min)	1m 17s
Test Suite (8.2, pgsql, 5-max)	1m 18s
Test Suite (8.2, pgsql, 6-min)	1m 9s
Test Suite (8.2, pgsql, 6-max)	1m 21s
Test Suite (8.2, pgsql, 7-min)	1m 19s
Test Suite (8.2, pgsql, 7-max)	1m 9s
Test Suite (8.2, agnostic, 5-min)	23s
Test Suite (8.2, agnostic, 5-max)	28s
Test Suite (8.2, agnostic, 6-min)	25s
Test Suite (8.2, agnostic, 6-max)	45s
Test Suite (8.2, agnostic, 7-min)	31s
Test Suite (8.2, agnostic, 7-max)	31s
	31m 9s

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