Now is as good a time as any, make sure you water them in well.

Easy to raise from seed if there is any left on your plants.

I have sweet Williams in garden with their seed pods still intact, can I remove seed pods and sow in seedling tray to overwinter in my cold frame?

Not tried that. i sowed in spring.

Hi Amsterdam if seed pods are ripe you can remove but I'd store the seed (not the whole pod) until spring as Stera says.

Thanks Moon_growe and Steragram.