im cooking a london broin in a casserole dish in the marinade how long do i cook it for if the oven temp is set at 350

I took a guess and cooke the two of em for 30 min on 350 and it turned out tender n juicy as can be.

First, how much does it weigh? If it's cooked in a wet marinade I'm guessing an hour to hour and a half. But what you really want to know is the internal temperature. Probably you'll to reach 140F in a thick part of the meat.