I've only grown one type - I think it was called Tarpy

or something like that.
It was delicious, even at the end of the season, when it had a flower spike about 3' tall. We just kept picking it right through.
I don't know if that will apply to all varieties, so I guess you'll have to pick and see. You'll be able to tell as soon as you pick it if it's going to be unusable - and your chickens will think it's Christmas.
Does it bolt because your higher temperatures? Maybe sowing it as an autumn crop might be better.
We've tried a quick growing oriental cabbage called Kometsuna, this year. It quite clearly says it will bolt in high temps so to use it for early spring or autumn. We thought it would be perfect for our short season. Guess what - it all bolted. And we've got no chickens! We'll try again in the autumn but I fear we just won't be able to give it the right conditions. So we'll just pick the leaves like a cut and come again, until it gets too stringy (about a fortnight!)
I crossed with Ina (hi Ina - lovely to see you

). We grow spinach beet every year and that lasts all season, no problem with toughness. But, of course, both Ina's and my growing conditions are very different to yours.