Yup that's actually a tradeoff you have to consider in the game, putting more power into the engines speeds up how long it takes to make an FTL jump. So if you don't think you can beat the ship you're fighting, it can make sense to put all power into the engines to try and jump away before they destroy your ship. Turning off life support still leaves you with the air currently in the ship which lasts for some amount of time depending on how big your ship is/how many crew members you have/how many hull breaches, open airlocks, or fires there are.