In response to the pandemic of COVID-19 and in lack of pharmaceutical solutions, many countries have introduced social and physical distancing regulations to contain the transmission of the virus. These measures are effective insofar as they are able to quickly change people's habits. This is achieved by changing the monetary incentives of rule violators but also by shifting people's perception regarding the appropriateness of socialization. We studied the effect of introducing, and then lifting, distancing regulations on the perceived norm regarding social encounters. We conducted an online incentivized experiment in France where we elicited the same participants' perceived norm and social distancing behavior every week for three months. We found that people shifted behavior and norm perception as soon as the government introduced or removed distancing measures. This effect was fast acting and long lasting. This is informative for future interventions, especially in light of a possible COVID-19 recurrence.