Back when we had rose shows (and a local society) for the most part, timing wasn't an issue. The early once bloomers were usually over by the show, but not always. Albas galllicas, and damasks were there in force.

The only OGRs that should keep are HPs.

Thanks mad_gallica.

I won several National Dowager Queens with R. moschata. The key was to keep the plants happy and producing new canes all summer long.

See if you can find any papers written by Dr. Henry Najat who had a huge collection of OGRs (I think he lived in Wisconsin ). I looked him up and I did remember that he passed in 2022. Maybe there's a archive for that part of the world of roses?