You mean the space between the further apart ends of each paver in a soldier course?
For us 1/2" is the max. We don't have a formal guideline, but I was considering doing so.
We've also cut projects where every paver in the soldier course is cut snug against the next piece, but I don't think that is the expectation of the client; to that point, I don't ever recall having had a complaint about soldier course spacing.