I would for sure put the vet on notice, especially since it is getting near the end of a work day. Or you can lube up and stick a couple fingers in there and see if you can feel a kid, and the position it is in.
My experience with these older does, if they have needed help in the past they may need help again. That is why I asked about her age.
to directly answer your question, They can have amber goo for several hours before going into hard labor. Did she push last time, before you had to call a vet out? or did she just stand around looking like she should be in labor, and never really pushed hard?