Three hours is plenty. You walk out of customs, look to your right and recheck is basically right there, memory serves. The domestic checkpoint is on that arrivals floor, follow what the signs say. However, unless something's changed in the last few years, there's not much going on airside, at least in T1 domestic. It's basically just a room with a small shop and such. Burn an hour in the airport mall or something, unless you're super out of it from your flight.