Thanks for writing. The best time to prune most roses is early spring --- around March or so.
The exception is wild roses that bloom in spring --- if they bloom before mid-June or so, you'll need to do the pruning right after they finish blooming for the season or you'll risk sacrificing the next year's flowers. (And if you don't mind losing flowers, then you can go ahead and prune them back in early spring.)
---Justin, Senior Garden Editor, BHG.com