Dates calclation

Question

I have 3 sets of dates 1st set 1-5 days 2nd set 6-10 days 3rd set 11-Infiniti *NOTE ALL DATES DD/MM/YYYY I need if I give START date 1/03/2020 END DATE. 4/3,/2020 ASSIGN IN 1ST SET NEXT TIME IF I GIVE 5/03/2020 END DATE 9/03/2020 ASSIGN ONE DAY IN 1ST SET REMAINING DAYS 2ND SET VICE VERSA