With pressurized CO2 on a solenoid one wants two separate timers. And you want appliance timers not light timers. The difference is appliance timers are grounded.
The reason for two is the solenoid should turn off the CO2 half an hour or an hour before the lights shut off and it turn on the CO2 about half an hour after the lights come on.
For anyone looking for timers, who can wait, I always purchase mine December 26th. At least 50% off and sometimes 75%.