This is not the case. I've imported saves in the past due to fatfingering or whatnot, and I distinctly recall using Time immediately after an import on multiple occasions. Double-checked just now after seeing the 15min message, and that is indeed the case.
#Time claims you need to wait 15min after an import to use it
hexed hare
cobalt marten
it was the case before the rework of the time code, i guess plat just didnt care for the new one, since even with the 15min wait it's still exploitable, you just need to wait longer (and also later in the game ||you get it right automatically, even though the quarks you get from it are more or less irrelevant||)