Yes if it's an all-in-one regulator chances are the solenoid is shut when not plugged in ("Normally Off"). Therefore, without a PH controller you will need to either leave it plugged in 24/7 or plug it in to a timer to control when the CO2 goes on and off.
To leave CO2 on 24/7 or not is a debated topic, people have wonderful results either way and problems are rare with either method. I leave it on 24/7 now, I use to turn it off and on but noticed no apparent change to plants, PH or anything else so I figured no use having the extra equipment if it's not doing much in my tank. You'd be best to try it out for yourself, go with whatever gives you the more stable CO2 levels. Lately Tom Barr has been claiming that PH swings due to CO2 changes do not effect fish as previously thought, if this is the case then you don't run many risks at all experimenting with the two methods.
Hope that helps
Giancarlo Podio | 
Co2 regulator and Soleniod valve question 
Linear Mode
