Mine has not long finished having hers. At least, I think she is finished! :rolleyes:
Her biggest gap was between the first and second pup, then no. 3 came almost immediately after no.2, so do keep a look out while cleaning each one.
I spoke ot my vet befor she'd had the first, and they said as long as she wasn't straining/pushing unconstructively (eg. pushing hard for 20 mins with no birth) then they weren't worried. I even rang them a little while ago to check all was Ok, as Mum is still panting, so I wondered if ther are more whelps to come, and they said the same, and it's not unusual for one to pop out the next day.
If in any doubt, ring your vet back though! Good luck!