Weddingbee boards

This might sounds like a math problem.  We are providing a bus for people to get from the hotel to our ceremony/reception site and back. The ceremony is at 4:30 and the reception ends at 10. The hotel is five minutes from the venue. If we need two trips (as all guests may not fit on 1 bus), what time should the first and second trip leave the hotel to get to the venue before the ceremony, and what time should the bus make its first and second trip to bring people back to the hotel? I dont want guests to wait around too long before the ceremony, but I dont want people filing in as Im walking out either!