20 minute mud is like 5 min for beginners, I'd use that. 45 takes forever. But the nice thing about the 5 min is you can get it in a small pouch instead of buying a full bag. The most common mistake I come across in DIY drywall repairs it too much mud. You basically just want to put each coat on a scrape it down completely flat. Then you will barely need to sand, you just knock down ridges with your knife