I'd like to use a timer because a simple acceleration switch would trigger when the acceleration becomes negative, which is right after the engine burns out. The rocket has to coast to get any altitude. The burntime of the engine is only ~1 second. Flight time is around 20 seconds, so a 10 second delay would deploy the parachute shortly after apogee. It seems easier to figure out the time to apogee. A magnetic apogee detector is expensive, and a flight computer is more expensive, and heavy. Timers are usually used as a backup system for rocket recovery.
The ignitor for the ejection charge runs on 4 AA batteries in series. To save weight, I'd like to use one of those little 12 volt batteries. It looks just like an n-size, but it's not. I figure I will use that
12V battery to run the timer which will operate a relay to complete the ignition circuit. Hopefully this is enough info.
Thanks for the help, and I apologize for being such a newb!