Our answerers are looking to "help" more often than they are looking to "do an entire project for you for free".
Jump into this project yourself, when you get stuck on ONE specific hurdle, post that ONE item as a forum question.
Show us what you've tried in an attached sample workbook and how it's not working for you. When you're doing the work yourself, just writing out a complete example question in a forum often points you to solution before you even finish posting.
Glad to help, and thanks for the feedback, but maybe I was a bit too quick and the formula needs some tweaking.
= TEXT(MOD(FLOOR(A2,TIME(0,30,0)),1),"hh:mm") &" - "& TEXT(MOD(CEILING(B2,TIME(0,30,0)),1),"hh:mm")
So it starts within a half hour time frame as well. Like 7:45 to 9:59 is in the range 7:30 - 10:00