Oshani, I think it is really your call...
I have friends whose babies went to bed later and woke later (I think they went around 9-10pm, then woke around 9-10pm. This worked well with their lifestyle, so they stuck with it. IMO there's no point waking your baby at 7am if you don't want to be awake at 7am too!
Personally, I am cactus by 10pm, so that's my bedtime. That's why I've always made sure Natty is asleep by 8pm unless we're out. Like others have said, for us her night bedtime depends on when she woke from her afternoon sleep. She needs to be awake by 4pm, otherwise it is very difficult for her to go to sleep at night until closer to 8.
Does Oscar sleep well during the day?
Jordie, I'm sorry but I don't have any suggestions for you, other than it would seem that's a fairly common theme among 4mo babes! Hang in there.