I've recently been informed of a practice of visiting a person who has returned from Hajj. There are three days to visit this person (similar to visiting the relatives of one who has died). Is this from the Sunnah to do this?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

There is no evidence in Sunnah that specifies a period of time for visiting those who return from Hajj or travel. But, such a thing may be among traditions and habits that people are accustomed to. So, it is better to comply with such habits in appreciation of the visited's circumstances, since he manages his affairs in accordance with such habits and customs.

It must be known that specifying only three days for offering condolences is not proved in the Sunnah.

Allah knows best.