Well, I've done part-time 3 times. Would love to do it again.
It didn't take much prep at all, really. Once I got the go-ahead from work, and agreed on a schedule/ # of hours, I just did it.
It took about a month for the coworkers at the first place to get used to my schedule - meaning, if you need me to get you data for tomorrow's 8:30 am meeting, you can't come in at 3:30 because I leave at 4. I can get it for you at 7:30 am...otherwise, 1 pm.
One thing that I *had* to do each time - and 2 of the 3 times I was a manager - was learn to delegate. At part time, all the important stuff got done. But the stupid little "make work" things that I did because it was easier than training someone else? At part time, I totally trained others to do them. It was good training for the younger folks too.
As a manager at part time, I had to be really organized with planning and scheduling projects, and I did have to check my email at home. We were a 24/7 operation.