"tim" writes:

I can't say I've ever see a timed ticket (except a full day)
that is defined as unlimited rides.

In most of Scandinavia, that's the normal case, as far as zonal ticket
systems are considered (eg all the capitals). It varies whether the
time limit applies to the last boarding or alighting, though. For
instance, in the regional system of the Helsinki area, single tickets
(cash or Oyster-prepay-like) are valid for unlimited travel within the
appropriate zone(s) for 60/80/100 minutes plus whatever it takes to
reach the last stop of the line after that (or max 1 full loop on
circular lines).