Yep, that's pretty much normal. My guess is that the A/C evaporator has a vary large mass (a cold plate, maybe) that takes a while to cool down, but once it gets cold it stays cold. This would be useful to help keep the air temp very constant as the compressor cycles on and off. I know that on some cars you can feel the temp of the air rise and fall as the cycling occurs.

Here's a neat thing to try as well: Next time you park the car after running the A/C, turn off the engine and then press the REST button. You'll notice that the air coming out of the vents stays cold long after the engine is shut down.