I always thought Nemesis was around for a few days before the events of 3. Mainly because of the way Brad's acting in the beginning of 3. Brad's exact words were "He's after STARS members, there's no escape!". Now, I know this is chickenheart and he'd run for the hills even if Nemesis wasn't attempting to kill him but was instead chasing him with a batch of freshly made cookies shouting "EAT THEM", but to me that line made it sound as if Brad had been chased by Nemesis for at least a few hours. Also, this is Nemesis. He isn't some all knowing all seeing entity. He'd have had to search for the remaining STARS members. He only came across Jill by chance whilst he was hunting Brad. How long would it have taken him to find Brad?