With the cell selected, click on Format | Conditional Formatting and
choose Formula Is rather than Cell Value Is in the first box. Put this
formula in the next box:
=cell_ref>=1
Then click the Format button, Patterns tab and choose Red, then click
OK. Click Add to set up your next condition, and choose Formula Is and
put this formula in:
=cell_ref>=16/24
Click the Format button and choose Orange on the Patterns tab, then
OK. Click Add once more, choose Formula Is and enter this formula:
=cell_ref>=8/24
then Format button again and choose Yellow, then OK twice to exit the
dialogue box. cell_ref is the cell you have selected.
You should note that Excel stores times internally as fractions of a
24-hour day, hence the values 1, 16/24 and 8/24 above. I'm guessing 8
hours for the last one, as you missed this out in your post.
Hope this helps.
Pete