They should be fine for 3-4 days if you keep them moist but not too wet and in good light. I would open up the pack and stand them up to stop them rotting off but they will need more watering if you do. Best in a greenhouse if you have one, otherwise a windowsill. If it is south or west facing you may need to provide some shade if it is very sunny, especially for the fuchsias. (You can put them outside after the frosts have finished, gradually getting them used to cooler conditions, but it is too cold for them in the uK at the moment.)
Welcome to the forum Not much you can do really, they will be fine in their trays, just keep them watered preferably by sitting them in a tray of water. Also I assume you have a protected spot to keep them in.