It's better to dodge the lightning bolts in smaller groups that way you don't get mentally overwhelmed. When I did mine, I dodged the bolts in groups of 20, took a 2-5 minute rest, then continued.

Once I reached 200 I kept on going until I got up to 240 just to make sure. But even by then I wasn't satisfied so I kept on going.

I stopped taking breaks when I reached over 500 and was able to make it to 641 when I finally got hit.

So my record is 641. I could have gone more if I had rested.

You also need to have a "no encounters" weapon for any of your characters.