No reason not to adjust it in place. You'll be happiest if you go the timing light route, but yes, you can turn it a little as it idles, after loosening the hold-down bolt, and you will hear the engine change. Move it one way or the other, see how it sounds, and use your hand to push the throttle linkage and rev the engine. When you find a spot where it seems happy, both idling and reving, tighen it down and go for a drive.
If it seems better, great! If not, you can keep tinkering until you're happy.
Common wisdom is for the timing to be advanced to the point where you get a light "pinging" on hard acceleration. Pinging is hard to define - I'll let others jump in. But when you find it, some people leave it there, others back it off just a smidge. Then you're at optimum timing.
Good luck! Sounds like you're making great progress.
-Michael
