Rule: There can be no more than 14 hours between rest periods in any 24-hour period
To ensure that work periods are restricted and rest periods are spaced appropriately throughout the day and not simply stacked together, this rule was introduced to set out the maximum number of hours a crew member can go without a rest period.
Essentially:
The crew member cannot work for more than 14 hours consistently without a rest period within any 24 hour period
The 24 hour period is not specified, so any timeframe can be taken.