the average stuff. high amperage (for instance, something able to withstand 30 or more amps), multiple timing points available if used for watering or CO2 or fans, ACCURATE timing (no guesswork), non-digital (always less to break) and something that will continue to run on batties. The last thing I think is nice cause if your power goes out, then you dont need to reset everything, stays on the clock.

Possibly a central timer with multiple timers in one would be nice.

All of these things are already made.