In the Conditional Formatting setup for the cell in question (I used A1
for this example), set the dropdown to "Formula Is" and enter this
formula as the condition:
=A1="x"

Then apply the desired format. If you don't mind an outside opinion, I
prefer your first example above, which shows the 8:00 slot twice. That
seems more intuitive, and may be helpful for your non-Excel friendly
user.