Several months back we had a small discussion of using a timer to turn things on after a specific period rather than turn them off as most timers are designed. We used the term countdown for the ones we found but found none to "countup" to turn the power on after a specific time.
Maybe there was an obvious solution that we overlooked? I have a cheap timer which has now failed and that leaves it open to experiments.
This is the standard cheap mechanical timer that we see so often.
This is what we find inside. A simple mechanical link to operate a microswitch. The micro is what I circled in red. A pretty standard microswitch that sells for a under a couple dollars, it is a SPST to open or close one side of the power.
The switch just rests in the box on a couple plastic pins so that it can be pulled out very easy. So if we want to change from turning power ON to let the timer turn it OFF at a specific time to letting us set how long the power is OFF and then the timer turn power ON, we just need to change out this microswitch.
If your timer has a NC, changing it to a normally open will reverse the way it handles power.
Or with a bit more fuss on fitting the extra contacts into the space, one might add a switch of this type and have the option of wiring it either way.
Parts Express SPDT Snap-Action Standard Micro Switch with Lever
If I remember the question, there was a desire to turn filters off during feeding and let the timer turn them back on after that to avoid us forgetting?
Maybe the best solutions are the simple ones?