If its six weeks since they finished flowering, you can dig them up and either pot up or replant elsewhere immediately. If you pot them, make sure they're back in the ground by end of August, if you don't want to keep them in pots.

I don't work religiously to six weeks, I watch for the tips of the leaves to start turning yellow.

This means the bulbs have had their fill and the leaves are superfluous!

Having said that the time lapse from flowers dying back and this stage is usually around six weeks.

In other words I let the plant/ s tell me!