[css-values] Time type does not specify if unit is needed for magnitude of zero #4569
Description
Lengths allow unitless 0.
Angles note (in css-values-3; as I read it) that "0" means zero degrees from North/up in certain extant properties, but that new properties will always require the unit.
The definition of the <time> type does not specify either way.
We now have divergent implementations. Safari allows unitless specification for durations with no magnitude, Chrome and Firefox do not.