I'm not an expert, but from what I've read you should wait until the leaves drop, then wrap them. Several people around us (here in 5b) have wrapped their maples with burlap. I haven't seen them twine-in the branches, though.

Are these baby maples and curious what cultivars they are.

Curious so people know to stay away from them. Zone 6b is pretty solid for JMs.

I've lost plenty but still have plenty but I'm in zone 5a and haven't burlapped anything before.

Whass, sorry for missing your reply. The maples I lost were all in the landscape:
3 year graft - kamagata (completely dead)
3 year graft - beni maiko (died back to trunk, tried to leaf out and failed)
1" caliper sango kaku (completely dead)
1" caliper shishigashira (Died back to trunk and survived -- but a tiny 3-year graft sited elsewhere had no damage -- probably because I protected it from the wind)

A number of other trees showed no damage:
Inaba shidare
Osakazuki
Seiryuu
Viridis

Plus a bunch more in pots that were sheltered and mulched -- didn't lose any of those. That's why I wonder if it is the wind that is killing things.

Sango kaku seems to have a poor reputation for cold hardiness. I replaced it, burlapped it this year, we'll see. I decided not to tie the branches -- just staked and wrapped.

What grafted Japanese maples get a lot of is bacterial blight, 'Sango-kaku' in particular is notorious for turning black. Since you are getting variable results I wonder if this is really what your problem is and not winter cold.

That's definitely consistent with what I experienced with sango kaku. There were no problems until late winter though, so wouldn't you suspect it was stressed by the weather?

Burlapping the trees slows down the desiccation of the trees' branches and trunks from the wind, and minimizes the effect of frost cracks on the trunks.