All I can say is that as long as it works, there's no problem.
I guess a too big cap will smooth the sq. wave too much and a too small will not filter a lot of voltage ripples.
I often see 22 and 33 pF so I guess 22 would work good. This is not the best mod to do tho. IMO Building a XO clock circuit like Kwak or Guido clock is a better option. If your goal is to get low jitter, then it's the way to go.