I would say you can harvest them now. Personally I'd pick a dry day, and snip but keep a bit of the scape on them, lay them in a dry coolish place indoors on a tray and let them finish opening slowly drying down still on the scape. That's what I'm going to do this year, similar to the first year I got bulbils and I think they were my best quality.
Some people harvest the whole plant and hang it, but (in our climate anyway) it's overkill. Yes the bulbils keep growing but the moisture in the scape is enough for that. The ones that were hung whole at the farm had some green sprouts on them, and I had the same thing when I put cut scapes in water. I think the moisture in the scape is more than enough to let them grow full size, and you want them to start curing or drying a little at some point to be ready for planting. When they're fully opened, you may snip off the last bit of the scape to get them to start drying.
On the other hand while many methods work more or less, someone more experienced than I may be able to tell you the BEST method.
