I believe Henry and others also said, if you leave a scape or two on, they show when the rest is ready to harvest - when the scape stands fully upright. I don't think mine have ever got to that point but our weather is always threatening to turn wet and so I tend to err on the early side. Excuses, it's true, I just can't wait to get my hands on em.
An advantage of early harvest for a home gardener, it's said to improve keeping quality. I'm still eating porcelain garlic, still good ten months now from the harvest date.
Excuses, more excuses.
Down side is bulbs will be smaller of course, the earlier you harvest.
And somewhere in the middle there's "just right"....
Posted the same time as you, TomNJ. Sounds like you have the "just right" figured out!