If you mean 2 FP's with approximately simulateneous time windows, this generally doesn't happen.
However, I've been able to get FP's on one ride, and when the time window was still active but about to expire I was able to get another FP. I don't know how WDW's programming works with this, but I'm assuming the less popular FP rides will probably have a more lenient time window of when you can get FP's while another FP's window is still open.