When you say its going to freeze, do you mean you're going to have a frost? I don't know what Zone you're in, but it seems unlikely you'll be going straight from cool to the ground freezing solid in a day.
Physalis pruinosa is a frost sensitive plant, obviously, but if there's going to be frost tonight,do not pick your ground cherries - cover them with a tarpaulin or something to keep the frost off, lift it tomorrow, and replace and lift each night if its going to be frosty, until your ground cherries are fully ripe and falling off the plant. More information is available in this article: Tutorial on How to Grow and Store Ground Cherries (Physalis pruinosa).
It is possible to pick them a little under ripe, and they should ripen off indoors in the same way as tomatoes, but it's much better to let them ripen on the plant than off,so just keep the frost off them. The greener they are, the less likely to ripen off fully indoors.