The earlier the better. They close at 4 p.m.
From September through June, the visitor center is open from 10:00-4:00. It is closed on Mondays unless it is a holiday, then it is open from 11:00-4:00. Holidays for 2018 include Easter Monday and Memorial Day. For the months of July and August, the visitor center hours are: Tuesday-Sunday. 10:-4:00 Monday. 11:00-3:00 The park itself is open from 9:00-5:00. A walking tour of the grounds is listed as taking 1 1/2 to 2 hours
The parking lot and buildings close at 5 pm. If you are interested in just seeing the physical mission. You could walk through the buildings in an hour. However, if interested in the greater mission property, then give yourself at least 2 to 3 hours.
Thanks! Your answer is awaiting moderation.