Correct handling of time in plot_traces

[alejoe91]

Fixes #3324

[JoeZiminski]

It would be super nice to have tests for this as it's a little confusing as there are a lot of possible use cases to keep in mind. I think there was some discussion to avoid adding tests for widgets until a big widget refactor that was coming. Maybe we can make an issue to track these tests-to-add, otherwise adding tests now would be useful as they will catch regressions introduced in the impending refactor!

[alejoe91]

this was fixed elsewhere