[Tagging] units and notations for maxstay

[Tobias Knerr]

On 20.02.19 00:46, Warin wrote:
> On default units ..

I don't think there's a single unit that would be the obvious default
for maxstay, as both minutes and hours will be common. Omitting the unit
will lead to misunderstandings in that situation.

Therefore, I would define no default, treat missing units as a mistake,
and encourage people to always explicitly write down a unit for maxstay.