It takes about an hour and a half, using the purple rollers, which is the same time as with my Lady Dazey dome dryer. The soft bonnet dryer is much more comfortable to use, though. At first I had a problem with uneven drying: the top and front used to be still damp after the rest of my hair was dry. I figured out a way around this: instead of attaching the bonnet with the hose at the nape of your neck, put on the bonnet with the hose just above your ear, and you'll get better results. If you find the back is still a little damp, then just readjust the hose's position for the final ten minutes or so of drying. Or, you can have the hose at the back for half your drying time, then switch it to the front for the second half, or wherever is best for you.
Now that I've figured this out, I want to give my 2.5 inch red rollers (they're a lot larger than the purple) a second try. I tried them once before, but the bonnet was so crowded with my head full of them that the air couldn't circulate properly with the hose at my nape, and the top and front of my hair didn't dry. Hopefully, that will cut my drying time down even more when I'm in a hurry.