Right, the time that you need to be concerned is if:
a) she is pushing (straining) constantly and the sac doesn't appear
b) if a sac partially appears and after 20-30 minutes the baby still hasn't been born
c) if you think she is very distressed and exhausted
If these things happen, you will need to call your vet straight away. But more often than not, the births are generally straight forward.
If your girl is quiet now and cleaning herself and seems happy, then just stay with her and monitor her. The thing about births is that no 2 are ever the same, some queens will start delivering very quickly after contractions start whereas it can be hours with others, but so long as your girl is fine in herself, then it should all be okay
