I think I should formalise a few rules:
The winner will be the person closest to the actual time.
If there are guesses either side of the time (e.g. the actual time is 1.20.0 but we only have guesses for 1.19.9 and 1.20.1) then the LOWER time will win. Sorry if this seems unfair, but I've just realised that any other approach might cause multiple winners and, even more likely, multiple runners up. Think of it like Black Jack.
The lower time rule will also apply to 2nd and 3rd place if appropriate.
I would prefer it if everybody picked a unique time, but as we want to make as much money as possible for the charity, I'm not going to make it "first-come, first-served". Why stir up bad memories???
If there is a two-way tie for first place, then all the money for 1st and 2nd place will be split equally amonst the winners.
If there is a three-way tie for first place, then all the money for 1st, 2nd and 3rd place will be split equally amongst the winners.
If there is a two-way tie for second place, then all the money for 2nd and 3rd place will be split equally amongst the runners up.
If more than 3 people guess the winning time, or if there is only one winner and more than 2 people guess the runner up then we will split the relevant prize money equally.
I've just come up with this off the top of my head, so, if something doesn't make sense, or I haven't considered a possibility, please tell me now before there are too many bets so that I can revise the rules.