Modifying a lamp/appliance timer?
 

Does anyone have any ideas on the possibility of modifying a typical home lamp/appliance timer -- the kind commonly made with 24 hour cycles and often used when you go on vacation to turn lights on at night?

I want to modify one to have about a 5 minute cycle instead of 24 hours. Any suggestions?

It'll be much easier to make one (based around a 555 for example) than modifying. I suspect that the 24hr ones are based on a PLC or similar, so you'd have to change the firmware - but I haven't looked!