How do people decide when to cut their calabrese?

I have some heads that are good size now (after recent rain) - tennis ball size I guess. Only got half a dozen so want to make sure I get em before they bolt!

Pick them before the flowers start to open. They will usually produce spears after the main head is removed so don't dig out the stalks.

kingkano,
you're at a complete advantage here, in terms of that YOU have the upper hand.
By that, I mean, that you are the one who can decide to harvest, or not to harvest, and therefore you have complete control.

Watch your produce develop daily. If you look at it on Monday, and it isn't quite looking like something you'd want to buy and pay good money for in a shop, leave it another day, or two, or three, until you ARE sure that it looks absolutely perfect to eat.

I know it's silly, but I always 'eat with my eyes' before I cut any produce to put on the plate? That way, I rarely get it wrong, and can justify harvesting it.

I promise you, with enough practice, it'll become so natural, you'll not know you're doing it...! Really good luck my friend.X.

Thanks guys I'll keep watching and try and time it right they seem to grow a bit every day! Never had much luck with them before so am quite happy