Unless the dev releases more detailed information on how they approach their development process, it's difficult to say for sure. Bugfixing is probably the most tedious part of the process, but the time requirements depend on the number and types of bugs found. Beta testing is probably the thing on the list that will take the longest because the time the testers have with the game is usually fixed and there may need to be another bugfixing pass after the test, depending on how it goes. Idk what the dev's personal development process is like, but I'd guess the testing period by itself would be minimum a week, and everything else is probably at least another week of work. The development process for a solo dev is highly personal, and can even change update to update for various reasons. My guess would be at least a couple weeks, but it could be less and I think will probably be longer. Since the dev had to take a long break for personal reasons, it might take them a few updates to get back into a rhythm too