Self-explanatory really!

I need to know how long I should make each round on my server to ensure stats are taken for each game.

GT typically scans servers every 1-3 minutes.

The percentage of total stats the scanner is able to see increases with longer rounds or map changes, or what ever the increments are which reset scores. Every 3 minutes would be the bare minimum, but you'd likely want at least 5-6 minutes if reasonable.

Okay, thanks!