That would also eliminate the issue with people camping in a first and continuously changing defenses so no one can beat them since you never actually get the line you prepped for. It would be good for both FP and Coli. Not sure how long the timer should be, but it would certainly limit other problems.
The guild leapfrog thing generally takes care of itself. A single strong line does not hold a coli position against those who should be beating you. Those leapfrogging might get higher rewards than they would otherwise, but they will be pushed down the ranks pretty fast.