Sounds alright; games on timers like that are usually pretty frenetic and that makes it fun.
A less cumbersome alternative is Sudden Death Spleef (invented by Named, I believe). Build a block maze one cell deeper than water level leading around a square and ending in a hole on the middle, and then build a standard spleef arena under that (underground). Players have to determine a winner before they get flooded out. It's a lot of fun.