This is a siege map I made in 2005. It's not my best work tbh. :P Still can be fun though. The Ready Room secret room is worth it!
Here are the times for the doors: 2 mins - Shortcut to the door room from marine start closes. 5 mins - The big door opens. 10 mins - Shortcut to the door room from marine start opens again. 17 mins - The siege door opens.
These may be off by a few minutes, because it's been so long ago since I made this.