According to flight status you should depart at 3:43 and arrive at 4:42..which gives you plenty of time... unless you've been given other info on ATC delays.

I'm going to assume you're on IAD-LAX departing at 5:25... it's at gate C8.. not too far from the train station. I'd say as long as you arrive at IAD and are able to retrieve your gate checked carryon (if any) by 5:05 you should be able to make it. Any later and you're pushing it.