Thanks for writing. Five to eight days is common for many hardy shrub roses, especially if your weather has been dry or especially hot lately.
You may be able to get your roses to last a little longer by spreading a couple of inches of mulch over the soil to help keep the roots cool and by keeping the soil moist, but not wet. But that's about all I can think of that may help.
---Justin, Senior Garden Editor, BHG.com