Should I lower the oven temperature or shorten the cooking time?

I just tried baking hard boiled eggs in the oven after hearing how great they were. It was MUCH easier than traditional boiling. However, despite people saying how delicious the texture was, they tasted over-cooked to me. They had a slightly rubbery texture.They also had brown spots on the edible parts of the egg that showed where they laid in the oven. I think this would make some people blanch if they saw brown spots on eggs I served them.

So I am going to experiment and try to get the texture better and get no brown spots. I was wondering if I should try lowering the temp or the cooking time first. Anyone care to venture an educated guess?