"Should" for what? What's your objective? No one can give an answer in a vaccum.
2-4 hours post application will give you peak levels. We always test trough levels for injections but for some reason everyone has passively agreed to test peak levels on the creams, and I've never seen even an attempt at an explanation for it.
I like to test both peak and trough regardless of protocol. I want to know the range I'm operating with. Especially with creams where if you're applying once/day, your peak could be 1000+ ng/dL and your trough 350ng/dL 24 hours later
