You can clear a t5 on 1 hour days if you focus on actually clearing the POI, it really is not to hard. I also find this a rather strange comment made here anyway, the quests are not locked to a timetable. You can take as long as you want. Night clearing a T5 is really not all that different from clearing it during the day in later stages anyway, most of them are feral.
With some basic strategy, night clearing ends up being exactly the same as clearing it during the day.
I don't find it all that difficult to find the last zeds either - it does show you where they are. Worst case scenario, go to the roof, get right over the point and dig straight down.
Aside from a known issue a few alphas ago where the last zed simply would not spawn and the occasional vulture finding them is not all that tough. I would say that while vulture spawns should stay, they should not count to killing all the zeds, the do fly away sometimes and force you to fail the quest. It is not prevalent enough to care all that much though.