I think the most I have ever seen is about 30 minutes? That was using slow fly props at very low RPMs.... I haven't been around all that long though. Maybe someone knows more.
Plenty of people have stretched it beyond 60+ minutes but the physics is working against you - the limiting factor being the weight of the stored energy (batteries) that you carry into the air - "law of diminishing returns", etc. The military use some tethered machines as observation platforms - they can hover in place more or less indefinitely by pulling power up the tether cable.