The honest limits. In one day from Rome you arrive late morning and leave by early evening, which is enough for the Basilica of St. Francis (lower church 6:00 a.m. to 7:00 p.m., crypt to 6:15 p.m.), the Spogliazione shrine, St. Clare's and the Porziuncola near the station (7:30 a.m. to 12:30 p.m. and 2:30 to 7:00 p.m.). It is not enough for the Eremo delle Carceri up the mountain, San Damiano below the walls, or the Friday and Saturday evening opening of the crypt for personal prayer from 9:00 to 10:00 p.m., which is the quietest hour at the tomb.
The town is steep and stone-paved, and tour buses fill the basilica square from about 10:00 a.m. to 4:00 p.m. in spring and fall; early morning and after 5:00 p.m. belong to residents and pilgrims. October 4, the feast of St. Francis, and August 1 and 2, the Porziuncola indulgence, are crowded by design. Mass in English is available at the Porziuncola on Sundays at 11:00 a.m.
Assisi is not a place of apparitions or a healing shrine; it is a place to pray where two saints lived. Pilgrims who want that come away satisfied; those expecting a program of events do not. For length of stay see how-long-should-i-stay-in-assisi, and for the hills see is-assisi-difficult-to-walk-around.