I'd make a disctinction between surprise or initial attacks and delayed actions declared during a normal combat round.
1) If no combat has yet occured, opponents are unaware of the PCs etc, then the setting up an ambush - with a trigger action - can be delayed as long as sensible. E.g. covering a door with a crossbow for 5 minutes may be easy, after 20 or 30 perhaps a persistence check is needed to maintain concentration (failure results in a level of fatigue from the concenration and adrenalin). If the bandit was surprised, then they suffer a -10 penalty to SR, so the PC will likely go first.
2) In normal combat rounds, then the delay action last only until the end of the current combat turn, i.e. when strike ranks reach zero. If an event does not arise, then the PC has wasted their CA. They can initiate it again next turn when the SR order starts over again.
I have seen an optional rule for a 'Delayed attack', similar to a parry action, where the PC declares the attack which is only triggered if a target moves close to the PC - say 4 or 8 metres.
Or, you could allow delay action to last until the beginning of the PCs next SR - in which case they will have lost their CA due to the event not happening / hesitation, and would need to spend another CA to keep delaying.
Antalon.
