When does the three-day prohibition on eating—starting at 7:20 PM on Friday—end, allowing for food consumption: at the beginning of dawn on Monday, or at precisely 7:20 PM on the same day?

It is not permissible for a person to forbid what Allah has made lawful for him. Whoever does so should consume what he has forbidden upon himself and offer expiation for breaking an oath, because Allah has made such a prohibition equivalent to an oath. As Allah Almighty says: ﴿O Prophet! Why do you forbid what Allah has made lawful for you, seeking to please your wives? And Allah is Forgiving and Merciful (1) Allah has already ordained for you the dissolution of your oaths. And Allah is your Protector, and He is the All-Knowing, the Wise﴾ [At-Tahrim: 1-2].

Scholars have unanimously agreed that forbidding what is lawful is an oath for which expiation is required. If the prohibition is for a specific period for health reasons, based on a doctor's instructions, then the person's intention determines the end of the period, whether it be according to the legal daylight hours or conventional 24-hour days. Intention affects the oath in terms of specification, generalization, absolute application, and restriction.