What's the best time control to play online in order to improve? I am an amateur, 33 years old, never took chess lessons, never played in a tournament. Last year I rediscovered chess and I am trying to improve as much as possible by reading books, watching videos and playing correspondence chess online. There is a small possibility for me to play over the board or join a club at this moment.

So my question is: what's the best time control to play online in order to improve better? I feel that 15-30min is too fast and there are very few players who want to play bigger times online. I like correspondence but sometimes I forget (over night) a bit the feeling of the game, lose the ideas or other stuff..

I am reading a lot of books but I want to practice more...
Thanks a lot!
This question will receive more opinionated answers regarding the time control, I will answer in perspective of an advanced beginner Chess player. Since you have said you are a beginner and never played in a tournament before, I would suggest you to have 1 hour or 45mins + 45sec increment time control. This is because of my previous answer here: Do longer games better your chances of honing chess skills?. Additionally:


When you engage yourself in a 1 hour time control chess game, you
are not under any pressure to make moves without calculation and
thus avoiding big blunders, this happens almost for everyone who
has not played against opponents much. 
You are also open to various variations for a move, thus allowing to
think at least 3-4 moves ahead of the next move(visualizing).





  I like correspondence but sometimes I forget (over night) a bit the
  feeling of the game, lose the ideas or other stuff.


Yes, Correspondence games will tend you to lose track of your positions, tempo, tactics etc since it may take 1 or more than 1 day to make a move. Almost 20-30% of the time either me or my opponent will lose because of this, even though having an advantageous position. But my guess is Correspondence game is relative to your memory power.

But remember that you also need to concentrate on the skills by reading books, solving puzzles etc. Playing with opponents alone will not improve your game because online games are just application of your skills not development.