How long before a baseball game might it be cancelled due to rain?

I’m supposed to be going to the Sox/Yankees game tonight at Fenway, about a 3.5 hour drive for me. Weather.com is predicting 100% chance of rain most of the day, dropping to 80% chance by 7pm (game time). How long before game time might they decide to cancel the game? I’m really not looking forward to sitting in the rain-soaked bleachers for 2 hours waiting for their decision… :-(