Your rest must be completed within the 24-hour period which begins when you resume work after a rest period,
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Example 1.
Start work 07:00 Monday
Finish work 20:00, 13-hour duty
Resume work 07:00 Tuesday
Full 11 hours rest taken within the 24-hour period.
Example 2.
Start work 07:00 Monday
Finish work 22:00
Resume work 07:00 Tuesday
Reduced 9 hours rest taken within the 24-hour period.
Example 3
Start work 07:00 Monday
Finish work 21:00
End of 24-hour period 07:00 Tuesday
Resume work 08:00 Tuesday
11 hours rest taken but only 10 hours are within the 24-hour period so reduced rest used.
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Remember the regulations make no mention a maximum spreadover or duty time. We only get the 15 and 13 people talk about because of the requirement for the rest to fit into the 24-hour period. Work 1 minute over 13 hours and you are using a reduced rest. This is probably what happened in your case, you worked over 13 hours, took 11 off and didn’t count it as a reduced rest so reduced too many times between your weekly rest periods.
The 24-hour period does not run from midnight to midnight but from when you start work to when you finish your daily rest; it can be less than 24 hours because a new one starts on completion of the daily rest.
Start work 07:00 Monday - start of 24-hour period
Finish work 20:00, 13-hour duty
Resume work 05:00 Tuesday - end of 24-hour period that is only 22 hours long and start of new 24-hour period.