Welcome back Liz, great to have you back around :)
This latest one took me a good 15 hours and was easily my quickest!!
As for selling yourself short on time, I always warn people who commission me, and also when I advertise, that it can take up to 3 months depending on my work load and time of year to have their drawing in their hands. When you do commissions, definitely set a generous time frame to do it in, If you tell them they'll have it withing 2 weeks, you're going to panic and rush it. I am able to sit back, have a good look at the photograph, plan the drawing, start putting undercoats on, and just potter along doing a couple of hours here and there when I feel like it, and still manage to get it done on time ;) PLus you can then sit it up on the easel and walk past it every day. You'll pick things out that you missed before, where as if you just sent it straight off, you'll miss out on finding little errors across the drawing.
Don't push yourself to take ages on a drawing though, jusr focus on an area at each sitting, get it perfect and if you get bored walk away and do something else rather than pushing yourself and hating it.