sorry for the late answer.
php will by default stop execute any script witch takes longer than 30 sec.
usually a script is executed faster than this, and the 30 sec is only a secyrity precausion.
how-ever some times the time need to be longer, expecially if need to doo long loops - e.g. same command into meny users (mass PM)
to overcome this php have a coomend to increase the maximum execution time, witch this MOD make use of - so in principle this mod may be executed for a longer time, how-ever some shared hosts disable this feature, so one user can't take to mutch CPU from other users if a script is runing berserk.
this is a snap from the code found in groupmsg.php witch I have included in the mod
//
// Increase maximum execution time in case of a lot of users, but don't complain about it if it isn't
// allowed.
//
@set_time_limit(120);
if your server does not support this php command, you either need to modify php.ini so it does, or only PM small groups of users