Is visiting graves at dawn for three days from the day of burial (فكَّة الوحدة - "breaking the solitude") forbidden or sinful?

Visiting graves is desirable at all times. If a specific time is allocated for it because it is convenient for the visitor, there is no harm. However, if it is allocated with the belief that it has a special virtue not established in Islamic law, then it is an impermissible additional innovation (bid'ah idafiyyah). Therefore, the custom of allocating three days after burial for visiting the deceased should be changed.