How soon after pollinating are we talking? I would say it just depends on if it's a heavy down pour or the sprinkler water really heavy. On rainy days I will pollenate in between showers if it quits for a short bit; if it's just light showers that is. If it's really heavy rains I don't. And we have turned the sprinklers on 2-3 hours after pollinating a few times. It's a 50-50 shot if the pollen has gotten down into the pistil or not.
I was told it happens almost instantly, I think Fred might have mentioned that...not sure. I know it takes a pretty hard rain to wash it off. Surprised me for sure. Even having been told this, I still panic if a get a rain shower, especially if it is 'the' cross ;-o