The best chance you have of winning a challenge is to wait until the last moment and submit a replay, even if you actually got the time a week earlier.
I am not going to explain why because it is pretty obvious.
"Back in the day" this would be more of a problem and would lead to less back and forth battles and would contribute to inactivity.
It would also be more of a pain on a map like this, rather than a 30s map.