Use this:
T=Timer()
DO
Elapsed=(TIMER()-T)/1000
IF Elapsed=60 AND dog_not_fed = 1
HIDE OBJECT o_dog : REM here is the line where you'd make the dog run away, so use a move object command or something.
Elapsed=0
T=TIMER()
ENDIF
LOOP
Change the 60 in the "If Elapsed = 60" to whatever time you want in seconds before it runs away.
dog_not_fed would be set to 0 if the player has fed the dog, and set to 1 if it hasn't been fed.
I suggest reading TDK's tutorial on timers if you don't know how to use them, the tutorial is at
http://forum.thegamecreators.com/?m=forum_view&t=59347&b=7
Good luck!