Really varies quite a bit depending on how much use your gear gets, how its stored and how old it is.
A rain jacket will usually last me around 4 years before I start getting delamination issues.
That's with a lot of use and wearing a bino harness and a pack will be real hard on the DWR treatment.
1st year, I may wash it in tech wash a couple of times following hard use. 2nd year, I'll actually start applying DWR, probably 2-3 times that year + a couple of Tech Washes. 3rd year, probably 3-5 times for DWR + however many tech washes. Around year 4 is where I usually notice a bigger decline in performance.
Basically, you need to reapply DWR when water stops beading up. You can always do a shower test to see how well its holding up. Wash in Tech Wash anytime your gear needs laundering: if its dirty, been exposed to dirt or has been used hard.