well, it depends. First you have to know that the whole visit takes half an hour. Actually 15 minutes to get acclimatized while watching a video, then only 15 minutes to see the paintings.

I recommend to do your homework if you want to fully appreciate what there is inside to see in the chapel.

Some days you just walk there and you can get in with the next entrance (after having been forced to book anyway!). If there are a few coaches that they, then perhaps you won't find any spare place.

May is not that busy period yet, therefore I think evena a weeks or two in advanced would be enough.

Anyway, if you have to plan for your time, I suggest to book as soon as you know what your plans are!

In the past there was the possibility to go for a visit in the evening where they would give you extra time to stay inside. I do not know if the initiative is still valid. Write them to find out.

You probably already know the site:

www.cappelladegliscrovegni.it/eng/index_e.htm

grazie,ginopanino!

I just ordered the tickets for May 10th,online;very easy,with email confirmation immediately afterward.