Went to wait for 30 minutes, was asked “Resume task?” or whatever, and then it finishes six hours later.
I think the error may be that you tried waiting for a long time earlier, but you were interrupted. This prompts the game to save your waiting, just as it would with crafting, and attempt to pick up where you left off beforehand. This makes sense with crafting; if you get interrupted halfway through making a radio, you wouldn’t start from scratch just because a fire ant got in your shoe or something, but it doesn’t make much sense with waiting; it’s just there because waiting and crafting probably use similar code for time-skipping.
Oi! Devs! Stop using easy workarounds! 
I’m not sure, the longest I could’ve been ‘waiting’ before was during sleeping, as I never wait more than an hour.