maybe 40 days because my games usually last around 60 moves and I only have time to move every 12 hours. Some games may last like 80 moves.
Then, you will have to play in matches with current daily time controls. You should not play with this time control in case it gets accepted.
Many users seem to agree that it would be nice having an alternative time control that prevents extreme delay in daily chess. See also:
https://www.chess.com/clubs/forum/view/suggested-feature-alternative-time-control-daily
Still, agreeing on the details of the alternative is not that easy. For me, "all moves within 30 days" is not an option that I can support. I'm really a "daily" player: In most of my games, I make one move per day in the evening. This becomes infeasible if you have a long game and a fixed amount of time available.
My preference (as described in https://www.chess.com/clubs/forum/view/suggested-feature-alternative-time-control-daily) is clearly a time control with some (either Fischer or Bronstein) increment per move.