KDN that Arduino MPU unit is fantastic if a little overboard for a timer, your initial investment for the board plus extras to get it to the point where it could relay a solenoid and a pressure switch would probably be over a hundred I'm guessing.
Early someone was mentioning these SESTOS solid state timer units, offered on Ebay using OMRON relays inside, that are built in Hong Kong
http://www.ebay.com/sch/Relays-Timers-Counters-/78202/i.html?_catref=1&_ipg=200&_ssn=skiesmall360&_trksid=p3286.c0.m1538
He's offering them for $25
It seems if we're looking for a good timer on the cheap, the person early that actually mentioned this seller, was right on the head. The Arduino may I suggest seems as if it could replace a REEF KEEPER ELITE, which is a $600 dollar piece of equipment that I was planning to use to fully automate a garden but having seen the Arduino, it can do all those things and more.
Actually there's so many fields it could be applied to, air/heating/cooling/pool/spa/terrariums/coral/fish etc. It's actually asinine to comprehend just how much power one of those little units has plugged into the right equipment.