In my experience and opinion
- Having more time is not really an advantage when playing blindfold
- You have a clearly higher risk of blundering when playing blindfold
Let me try to expand on this.
- Playing blindfold in a single game for more than an hour for the entire game is a huge effort of concentration. Playing blindfold for two or more hours on a single game might be too much to handle, unless you have some special method or extreme stamina. So having more time isn't great from the stamina point of view.
- There is a clear risk of losing track of something (e.g. a pawn) on the board or forgetting to register one of the moves and later pay for this mistake. The risk for blundering is clearly higher when you don't see the board and the pieces.
My conclusion is that you will definitely play below your full strength. How much below, depends on how well trained you are in playing blindfold chess. If you play on two or more boards simultaneously, I predict that your strength drops even more. My guess is that you can come up to 80% of your full strength when playing blindfold (after a lot of training and practice). Even then, your risk of blundering will be higher!