So if the Celtics win on Friday they will have 6 days off and there is only one time in the finals where there is a single off day:
June 2: NBA Finals 2022 Game 1
June 5: NBA Finals 2022 Game 2
June 8: NBA Finals 2022 Game 3
June 10: NBA Finals 2022 Game 4
June 13: NBA Finals 2022 Game 5 (If necessary)
June 16: NBA Finals 2022 Game 6 (If necessary)
June 19: NBA Finals 2022 Game 7 (If necessary)
I think with this schedule, the Celtics should be fresh enough to beat the Warriors.