It totally depends on the pattern. I have a couple of patterns that are really easy and I have made several. In November I made 11 quilts in 21 days. 7 of these were baby size, basically Quilts for Kids pattern. 5 of them were lap size,(warm wishes pattern) one slightly larger than the others. The larger ones just had basically stitch in the ditch with a wavy stitch and I FMQ's the 7 little ones.
I have whipped up a lap size in 3 days. Others take me longer.