Who knows.

All kinds of opinions and theories. There may be some hard, scientific data out there that demonstrates the optimal time to cut them off, but I haven't seen it.

In general wait until they curl at the top and cut them off low. It is said that cutting them before they curl results in more energy being expended to regrow them. I think I saw this come true in my garden last year, but I have CRS (can't remember stuff) so I am not positive.

I also don't know if the bulb size is really affected noticeably by leaving the scapes on. I hear it is, but last year I snipped the scapes early, they regrew and I got lazy and left them.

The garlic was still decent sized overall.

I assure you that Elephant garlic is lots bigger if scapes are removed. Not certain if hardnecks are bigger or not since I always eat the scapes. It certainly takes energy to grow the scapes which could otherwise increase the bulb size.

I love eating the scapes, so I always look forward to cutting them off!