To be honest "Chrisox" I didn't know who you were & I apologise, I had not been given time yet to read your personal diary, so there was no intended personal insult here in this topic reply).
I thought that it depended on, what light & temperatures you reared them in (was I talking about the Alder Buckthorns?)
One thought was, to give by Government hand-down, responsible rearing licence to caring Butterfly Conservation members only (having made that financial investment), for scientific study, so that many did not throw wild sightings data, with reference to
Climate Change Indicator Species.
It looked to me a bit like yellow garden grass (Spring/Summer this year?) and flowering pyracantha? in the background (Was usually Spring).
Tatty Spring Wings if it survives hibernation.
Your butterfly emergence (if dated openly and honestly accurately) if released about this week, might go into hibernation at about the same time as other wild Brimstones & also might have it's Spring breeding or brooding performance, out of time with the wild leafing of the Buckthorn next year.
Wild emergence of the single annually brooded Brimstone butterfly from pupa was expected by someone, at the beginning of July this year (somewhere in the United Kingdom).
- Brimstone Larva May 30th 2020, Lincolnshire Nature Reserve.
Kind Regards