A formula to check whether "Start time" column is after "+12 hour" column

part of the answer depends on how those cells are formatted/entered.  For example is that 22:00 entered as just 22:00 or is it 2025-07-13 22:00.  Also, will the +12 always be the next day and will the Start Time always be the next day.  If yes like shown in the simple examples you can highlight which columns you want to get highlighted (e.g. just +12 hour column, or Start Time column, or the 3 columns from +12 through Start time, or maybe the whole sheet so the whole row will get highlighted). Then go to Conditional Formatting (on the Home menu tab) and select 'New Rule'.  Then select "Use a formula to determine which cells to format". 

Then you want to enter the formula based on the upper left corner of the range selected.  In this example I assume you have +12 in column B and Start time in column D and I highlighted cells A3:Z1000

The $D and the $B means always look at those columns while the number 3 means to start looking at row 3 and move down to the corresponding row as it scans the page.

You also have to hit 'Format' and choose how to highlight the cells (I chose to fill with red)