I deposited a larger sum of ETC to Poloenix (> 100 ETC) yesterday. It didn't show up in the first hour. Found this thread and got quite worried. I obviously wouldn't have sent it if I had read it before. Opened a ticket.

When I woke up this morning, the full amount was available! So it took a couple of hours.

So, deposits are working, but there seems to be some manual verification involved. Maybe my case was handled relatively quick due to the larger amount? Anyway, I will probably turn to another exchange next time.