At what point should I start looking at intervening?
I'm not super experienced at breeding and all the issues that can arise. I can say the longest I have had a female in labor was about 24 hrs. One of my girls this year dropped 23 one morning took a 12 hr break then laid 2 more the next morning. Last year I had a co-worker that lost her only snake. They had taken it to the vet and the vet told them she was constipated. Come home and a week later the snake lays a clutch. Two weeks after laying the snake passed because it still had 3 slugs inside her.

In the end it is your call as the breeder and what you are comfortable with. I know a lot of vets have very limited hours with the current world situation.