I just put the sample in a plastic baggie and put it in the refrigerator. Freezing destroys cells, and when thawed out, they burst. So your eggs are then destroyed and not really identifiable.

As far as sample amount, you usually want a teaspoon or something around there, but sometimes I grab the whole thing as I want to get samples from different "areas" in the poo

If you keep it in the fridge, it should be fine for a good 24 hours, maybe 48, but that's stretching it. Try to get it to the vet as soon as possible.