respawn time, its the number of seconds that will pass before an enemy that died will respawn somewhere on the map. POSSIBLE_VALUE is teh number of seconds you set for such a thing to happen, and then all enemies' respawn time will be that by default.
As suggested by the manual, if you set it to ZERO (0), then respawning will be disabled, no matter what you set it to anywhere else.
Typically this is setup in the config application that comes with BlizzABS and generates the 1st part of the Blizz ABS scriptset. It can however be setup using the command within events "Script..." and inserting the piece you listed above with 'POSSIBLE_VALUE' replaced with the respawn default time.
Does this make sense?
--J
PS_if I'm wrong, correct me please, but this is how I understand it.