Assalaamu 'alay kum,
We know it is allowed for someone who missed the janaazah prayer to go to the cemetery and offer it, even though the deceased has already been prayed over, like the Messenger of Allah (may the peace and blessings of Allah be upon him) did for the lady who used to clean the masjid.
Is there a time limit for this? For example, if a close family member who missed the prayer returns after six months, can he still offer the prayer over the deceased?
Barakallahu feekum

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.

Whoever misses offering the funeral prayer until the dead is buried may pray at the grave, and there is no difference in this regard between a relative and others.

The scholars differed in opinion about the duration that is allowed to perform the funeral prayer after the burial. The view that we adopt in Islamweb is that it extends to one month and this is the view of most scholars as stated by Ibn Qudaamah in his book entitled Al-Mughni.

Allah Knows best.