I was induced and when I was ready I WAS READY it didn't matter how dialated I was I just asked and they gave it thank goodness I didn't wait
I'm not sure but I don't think there is a limit, if ur feeling pain u get it that's what it's there for some women have very low pain tolerance. If It wears off u can always get another dose.
I believe 4cm before you can get an epidural.