Yes. These dates are interpreted as ISO 8601 dates, but times are not supported.
These parameters only affect the time slider’s default state. It’s also possible to view the inspector for a node, way, or area that predates or comes after the daterange, in which case you’ll see its geometry plotted anachronistically against the base map, somewhat helpful for making comparisons.
The time slider currently filters elements based on their start_date=* and end_date=* tags; the start_date:edtf=* and end_date:edtf=* keys aren’t supported yet.