Controlling valves the efficient way
I think for whatever control circuitry you end up using, you are more than likely going to need a second lower voltage (step down the 24VDC to 3.3-5VDC). So, if this was my project, I'd probably use a simple microcontroller. An Arduino board would work. This would be the easiest way to control the valve using timers and potentially having a pot to select different time delays. You could even throw in an LED for when the valve is on/off.

I just did a quick search and came across this: http://www.instructables.com/id/Controlling-solenoids-with-arduino/ Not sure how well it is designed but it could be a starting point for you.