Early in the game you will have to turn a launch key and then you have 1:30 to get to the rocket. It should be plenty of time. Work up the rocket till you see a ladder you can interact with. I waited till there were 2 seconds left on the clock then interacted with the ladder and it popped. If it doesn't pop right when you hit X on the ladder just reload the checkpoint and it will put you back at the launch key.