As a commenter recently noted, the Harvard Shuttle doesn't come to Barry's Corner. The stops closest to the Allston neighborhood are at the I-Lab and Harvard Stadium.
Here is the Summer schedule:
The Allston Campus shuttle runs mornings from 7am to 10am
In the evenings it runs from 4:15pm to 7:45pm
There is one shuttle every 30 minutes.
Between 10am & 4:15pm, sorry but there is no Harvard Shuttle this summer.