The respawn is not for enemies, but for platforms that fall or rise, but I get what you mean.
I tried this, the same thing happens, all the same platform type will spawn at the same time, instead of individually.
I set up a test area, with 5 platforms, I ran across them all, they all fell, at slightly different times, but they all respawned at the exact same time.
I need them to spawn 5 seconds after they are destroyed, so if one is destroyed and another 2 seconds later, the first will spawn, then 2 seconds later the other spawns.
I am at a loss as to why they do not spawn individually, they seem to just spawn all as one.