Adaptive timestepping. When using adaptive timestepping (the default), the times that the solver is internally doing have an uncertainty as well since its steps are determined by the ODE system itself, so it needs to keep track of the uncertainty in time.
Cool stuff, I like it when Julia makes new features for us 
. Would you mind doing a PR to GitHub - SciML/SciMLTutorials.jl: Tutorials for doing scientific machine learning (SciML) and high-performance differential equation solving with open source software. ?