[Monster[HD]]

Deleted

[Deskoft]

Very simple, set a timer

pawn Код:

SetTimer(Function, time[milliseconds], Repeat[True, False]);

Check this for more information.
That link, from the wiki, shows to make a message to the console, use SendClientMessage to send a message instead.
To know how many time, consider it's a millisecond, 1000 x 60 = 60000 (1 minute) x 20 = 1200000 (That's 20 minutes, put that in the time for the SetTimer function).
Hope I actually helped you.

[Deskoft]

Here: D_Messages.pwn, I created a filterscript for you.