Comment by int_19h

The precise formula, assuming that object was at rest at the event horizon, is:

τ = (2√2)·R/3c

So "fraction of a second" is only true if you're talking about relatively small black holes. For a supermassive one, it can take hours or even days for the largest ones.

But note again that this assumes no orbit, just falling straight towards it from rest. For orbiting objects it could take much longer depending on their velocity.

Also, this all is from the perspective of the observer who is undergoing the fall. From the outside, time dilation means that objects never actually cross the event horizon at all - no matter how long you wait, you'll see them as they were getting closer and closer to it, but never the actual crossing.