In hot weather (days with a max of >23C) the males tend to take a mid afternoon siesta before becoming nicely active in the early evening. Old males are particularly prone to do this. Late in the flight season they are often inactive during the mornings and are very much afternoon - or early evening - butterflies.
In the present weather conditions it is well worth looking for males from 5pm onwards, until about 7.30. The challenge, though, is finding where they are, for activity is distinctly localised and not necessarily in known afternoon territories. They move with the sun and congregate in discrete places - sheltered but sunny tree summits, gaps and corners, out of the wind.
On Friday, Savernake Forest put on an excellent evening flight during this period. I even had a male in fair condition come down to the ride surface (5.20). They are still going quite nicely in Savernake, but it is a 'late' site.