It certainly does seem to be both. However it's possible that the personal limit per time turner is specific to the construction of the time turners and is not an iron law of time travel. If they were constructed to have personal daily limit equal to the absolute limit ("Who would ever need to go back in time more than 6 hours in a single day?") that would explain it.

Alternatively, the characters are just very confused, but I would expect they have enough experience with time turners that they are familiar with their operating limits (in "ordinary" situations, anyway).