using that script you don't have to do much, only edit these:
new modes[MODES][0] = {
{"bare"}, // Another GameMode
{"barron"}, // Another GameMode
{"rivershell"} // Your GameModes
// You can ad another line for another GameMode
};
every line represents another gamemode,
add all your gamemodes there (currently you can see 3 gamemodes here: bare, barron and rivershell
#define MINUTES 5 // Change these to what ever you want.
#define MODES 3 // This is how many GameModes you want
these 2 things need to be adjusted too, change the 5 to 10, since you want to use 10 minutes
change the 3 with modes to the number of gamemodes you defined in the "new modes[MODES][0] = {"
and that should do the trick
oh and don't forget to add this script as a filterscript

but i guess you know that