I have worn a plug for all waking hours for 2 weeks. I had the medium Colt Anal trainer in place. A few things that I noted:
1) It is the neck size and length that is important for comfort, not really the maximum diameter.
2) I used a rope harness to keep it in place. As I moved, so did the plug. The rope would fall off of the plug. If I planned one rope to either side of the plug to form a pocket, that held it in best.
3) Remember that you will need to poop. You'll need to take it out, and put it back in. Plan for this accordingly.
4) Don't use the largest size you can take and keep it in for 24/7. Get used to it well ahead of time. Plan for a modest size.
5) I got a case of semi-diarhea during the wearing. I'm prone to it, your mileage may vary.
6) Exercise with it first to understand the feeling before going long-term. Bending over, sitting down and more active movements like jumping jacks and squat thrusts feel QUITE different when plugged.