In Halo 3, I thought I remembered being able to despawn objects using the "runtime max" setting. As an example, I would place five blocks, but set the runtime max to four. Each of the blocks would have successive spawn times (10 seconds, 20 seconds, etc.) so that, when the fifth block would spawn, the first would dissappear. With that said, I tried this about two years ago and my memory may not be the best. Have any of you had any luck with something similar?
Isn't possible now and never was. In invasion you can despawn objects at the beginning of each phase, but not for any other gametype.