I do mine March...:>)

climbers, HTs, and floribundas now, ramblers in the autumn.

I've done mine this week but I'm in balmy Berkshire. You can probably do yours in the next couple of weeks, depending on the weather

For new roses planted up - In the next couple of weeks - once the worst of the hard frosts are past, but if you're roses are already established & have been in the frosts all winter, then anytime now.