Let's be very clear about what's happening here. Respawn is not possible in SP. However, it is possible to fake it, as Armsty, Artak and I have suggested.
If you are trying to convert a MP mission to SP, while preserving respawn, one of the things you need to do is throw out the respawn script - as a whole, it's irrelevant. However, you may be able to salvage and use substantial parts of it in your fake respawn script.
If you want a 30s delay you'll need to decide what the player is going to do for that time. You may be able to use a specator script. Alternatively you could setPos the player immediatly to a position 30s run away from the weapon and vehicle depot.