Choose the length around your pace. The Porziuncola is 4 km down in the valley and San Damiano is about 1.5 km below the Porta Nuova gate, so hill walking and transfers can make a seemingly short list of visits fill a day.
Assisi · YOUR QUESTION, ANSWERED
How long should I stay in Assisi?
Two or three nights is a useful recommendation for a pilgrimage that includes the main basilicas, some quieter Franciscan sites, and rest. A day trip is possible: Assisi is about 175 km from Rome, roughly 2.5 hours by coach or about 2 hours by train from Roma Termini. A day trip offers a different, more compressed experience, and the train station is in Santa Maria degli Angeli in the valley, about 4 km below the hill town.
Sources & further readingBasilica of St. Francis: explore the basilica
Official sources cover institutional information. Suggested pacing and itinerary choices are planning guidance. Check current arrangements for your travel dates.