I do believe it is this (in the XEngine section):
; Sets the multiplier for the scripting delays
ScriptDelayFactor = 1.0
Setting to 0.5 would give a delay of 0.25 seconds, setting to 0.1 would give a delay of 0.05 seconds etc.
Do be careful though as fast timers have been known to make XEngine explode
Also, do bear in mind that if you are creating scripts using fast timers that you plan on giving away/using on other people's sims that they will either have to adjust this setting themselves or they won't run correctly.
ETA: The delay was hard coded into opensim quite a while back. It was found that multiple AOs on a region using fast timers did make XEngine explode and so the delay was written in. Since then hardware has come a long way so it may
be ok if you have superfastrapidhardcore hardware to run on. Although trying it will give you the answer