Playing long, well thought-out games is a good way to improve and enjoy the game. For me long is longer than 2 hours. Unfortunately it’s hard to find opponents that are willing to spend so much time on one game. Random people from OGS are likely to just blitz out their moves or bug you to move, which is not fun at all. So I suggest to use this thread for finding opponents.
I too prefer slower games. I was never good at blitz chess although my competition rating at slow match time limits was excellent. And I’m not getting any younger either .
Playing on OSR is probably your best option – and many (maybe even most?) players also are registered OGS players so you can play your league games on “our” server .
I would like the occasional game like this but would be hard pressed to find the time! I could only do it during my (UK) day in the week, never at weekends.
Again, OSR is your place to go. When in a league you are not forced to play at any specific time. You play whenever you and your opponent agree to play. Check them out (openstudyroom.org) and read the info about how their leagues work.