Conditional Formatting to compare the minute value between two cells

I have a spreadsheet that has two values; "Show Start" time (eg 20:30) and "Off Sale" time (eg: 20:25)

I’m using a large amount of data to check these values are set as they should be.

I’m looking to set a conditional format, to show if the "Off Sale" time is anything but exactly 5 minutes before the "Show Start" time, to check that shows are set to come off sale 5 minutes before the show starts.

EG:

Link to an example spreadsheet here

I am limited with how much I can change the data from hour:time format, as other users need to read the sheet in hour & time format

Tried a variety of conditional formatting custom formulas, less than / greater than values, but I’m not familiar with using hour & date formats enough to subtract 5 minutes from the Show Start value for example

>Solution :

try:

=(B3+"0:05")=A3