This isn't possible via a script. You'd have to make a source change in /src/map/guild.c::guild_invite. If you want to disable during WoE you can just do something like:
if (agit_flag || agi2_flag) {
clif_guild_inviteack(sd,0);
return 0;
}
If you are wanting to disable for specific times outside of WoE then you'll need to check with the timer.
time_t timer;
struct tm *t;
time(&timer);
t = localtime(&timer);
if (t->tm_wday == x && t->tm_hour == 0 && t->tm_min >= 0 && t->tm_min < 26) {
clif_guild_inviteack(sd,0);
return 0;
}
You'd need to change the x in the t->tm_wday to some value from 0-6 (Sunday = 0, Saturday = 6).