Originally Posted by
underfire
Where are you based? Under Australian rules you have one minute.
The pilot in command must commence a change of level as soon as possible, but not later than one (1) minute after receiving that instruction from ATC, unless that instruction specifies a later time or place.
This phrase is under Cruising Flight Levels section.
Isnt this phrase only used for a change of flight level, not an approach descent?
No, it's not. Cruising Flight Levels is chapter 3, not 4 (that contains the phrase).