A legal time restriction exists when the Lawgiver attaches an act to a particular period. A date chosen by an individual for convenience is not automatically equivalent to that legislative restriction.
1. Legally time-bound: ẓuhr prayer is linked to its designated time.
2. Legally unrestricted: certain expiatory duties are not assigned one specific day by the initial command.
3. Personal scheduling: choosing a day does not by itself rewrite the legal classification.
This matters especially for make-up fasts and vows specifying a day. Individual choice operates within the bounds of the pre-existing legal duty.