You are only betraying yourself if you lie about the time when submitting. The thought behind is, that you can see over time (amongst many trijams), how you evolve, how you get better. None of the other submitters takes close attention, maybe not even notice, what time you enter. Enter it for your own records, so you can see how got better, when you go through your submissions after 6 months or a year. This series is not thought to be a one-shot - participate once and never again. The makers of the trijam have settled a fantastic way here for us indie-devs to improve, to keep record, AND, at the same time, see sooooo many creative ideas from people with the same mindset, in the same situation as you are.