In line with my thoughts around The 100 Day Project, this was daunting in its scale and complexity (which seems funny looking at the final portraits all lined up like this because 18 isn't really that many), but I ended up tackling a painting or two a day and getting them all squared away in fairly short order.
I realize part of the challenge was this thing that happens when you do work for people you admire. There's an extra layer of paralysis that wells up around wanting to do my very best work to impress those I think highly of. This has happened when I've done guest comics for creators I've long admired or gotten commission requests from people I think are super cool. I suddenly heap a load of unnecessary pressure onto the creative process, assuming that I have to be better than I already am in order to deliver the goods.
This is bunk. People who hire you have hired you because they like your work. Just the way it is. I work hard to remind myself of that when my personal standards get in the way of delivering work on time because it's not good enough yet.
"Not good enough yet" is how you blow your deadlines. Don't fall prey to it. Remember what it is you love about creating and follow that instead.