This very useful comment has come from Julian Evans, author of Badgers, blisters and beeches:
He had mentioned to me that if we coppice Ash late in the winter it might not regrow for a year... so I asked him when was the best time:
"Probably best to coppice ash in October or November. This will then allow
the stump to 'overwinter' and it should produce vigorous coppice in late
spring, but no absolute guarantee. Ash is a strange species. Its seeds
require many weeks of stratification (moist cold) to germinate properly and
dormant ash plants/seedling kept in a cold store say until May before being
planted may sit all year looking lifeless and doing nothing only to flush
the next year! But, yes, an early coppicing is the best bet. That said, ash
is a very vigorous coppicing species."