Entering Washington from UAE, is covid test required and how many hours should be valid?

No test require

Although I didn't travel internationally, I wasn't asked for test results however, better safe than sorry...

Check with US Embassy and airlines. Every airlines has its own requirements.

There's a cellphone app in VA you're able to download to determine if you've ever been in contact with someone infected. I recommend you download it to be safe.

Had my test results but was never asked at the Airport