Cool. Thanks CK76. I've had a quick look at the Over 304 and I'll have a closer look in the morning.

Did you also see that I was struggling with Conditional Formatting based on values that are formatted as [h]:mm;@ in Column R

I also need to conditionally format column R. (which is formatted as [h]:mm;@) as:
0-250hrs = normal clear cell
250-280hrs = yellow cell
280-300hrs = Blue Cell
> 304hrs = red cell