Infinity days!
The timer is just there if people want to coordinate, but the submissions remain open indefinitely after the jam.
It's a personal challenge, so doesn't matter. It's in your local time.
For reference the dates are: 2 weekends + 1 week, as in: start your idea on the first weekend, chip away at it during the week, finish it on the last weekend. But again, just conceptually the why!