since you have only been left instructions on how to do a timed set,then there's nothing you can do.
All I can suggest is make sure that all windows and doors are closed,enter your user code and press the tick button,hopefully this will perform a customer reset,and try setting the system again,leave the property and let the timer run untill you hear two short beeps.
The system is now set,if you hear intermittent beeping folowed by a alarm condition,then enter the property enter your code and tell us what the keypad is displaying.
Don't worry,this isn't your problem,however your actions are.
If the reset doesn't help,then can you find any engineer/alarm company details,
Can you contact the home owner and let them know what's happening and let them advise you on what to do next.
e manno
May 2012