That depends. If you do not have a resident permit you need to move your car every 24 hours. If you do, then I believe you do not have to move your car unless there's street sweeping or snow removal. There might be a 48 or 72 hour rule but the last time I went looking for Cambridge's version the best I could find was the 24 hour rule for non-permit cars.

Source: https://www.cambridgema.gov/iwantto/parkacarincambridge

Relevant bit:

> Understanding When Meters are In Effect

> Signs at meters that say "Except" during certain hours and days, mean that the meters and the maximum time limit are not in effect on those days or during those times. For example, a sign that says "2-HR Parking, 8AM - 6PM, Except Sat & Sun" means:

> * you must pay to park there Monday through Friday, between 8:00 a.m. and 6:00 p.m., > * you may only park for up to two hours.

> Outside of the posted time, you may park for more than two hours and you do not have to pay the meter. Other signs (e.g., street sweeping) may require you to move your vehicle. Otherwise, if you have a Resident Parking Permit, you may park for the the entire time that the meters are not in effect. If you do not have a Resident Permit, you are still required to move your vehicle every 24 hours.