Rule: The hours of rest in any 24-hour period can be split into no more than 2 periods
To ensure that the crew member gets sufficient uninterrupted rest/sleep, this rule was introduced to limit the number of breaks that qualifying rest periods can be split into.
The more times a rest period is split, the higher the likelihood the crew member will suffer from fatigue through lack of suitable sleep.
Essentially:
The crew member must receive a minimum of 10 hours rest in any 24-hour period
The 10 hours must be split into no more than 2 break periods
Where the largest rest period must be 6 hours or greater
The 24-hour period is not defined, so any timeframe can be taken to calculate this rule.