Did you consider having first-class support for rest between sets? It's certainly possible to model it with metadata, but I imagine it's a very common thing to want to include.
I hadn’t yet considered it just because the metadata solves my use case of uniform rest across all sets. For varying rest periods, I can see how metadata would be suboptimal. I’ll do some noodling on this and see if there is an elegant way to make this first class. Thanks for the feedback!