Three days, 2 hours and 45 minutes.

Seriously ... there is no way to answer this. There are way too many variables, the biggest of which would be how much water is leaking into the house.

If you have plywood, even better! All you need to do is climb up there and have a look at the plywood. Does it have a drip?
Insulation only, you have to wait for it to soak through.

Do you have or suspect a problem with your roof? Waiting for a drip from the ceiling may not be the best tact to take.
Even with insulation only, it can take a long time for a slow leak to show through to the room below. The water may evaporate or stay absorbed between rains.
Also, roof leaks frequently do not manifest themselves directly below the leak itself. Many slow leaks will travel down a rafter or other structure towards a low point and drip from there.