Question about capital gains exclusion on primary residence

[Alison S]

Question for the tax pros out there.

If someone inherits a home from a trust after death of the owner, and the home is their primary residence, does the two year period to exclude capital gains on the sale of a primary residence start from the date of death or the date the house was distributed from the trust? 

For example - Mother dies May 1st and house is in a trust, leaving home to son  who is living there.  But the deed  is not transfered to him until November. 

The son decides to keep living in the house for now.   When the son eventually sells the house, does he have to wait 2 years starting from May or November to get the 250k primary residence capital gains exclusion?