والنوع الثاني: ما يكون الوقت معياراً له، وذلك مثل الصوم؛ فإنه يتقدر بالوقت وهو اليوم.
The second kind is a duty for which time itself is the measure, as with fasting, whose extent is measured by the day.
Unlike a prayer, a legal fast does not consist of a short act that can be completed at some point during a wider period. Its required abstention extends from dawn until sunset.
Container versus measure: several prayers may fit into one ẓuhr interval, but two distinct full-day fasts cannot both occupy the same religious day as separate complete fasts.
Consequently, a day legally assigned to a particular fast does not have the same room for competing acts as a prayer time.