Hypocampus is a site powered by Cortexio.
Last Christmas, 2018, Hypocampus had recently added a paywall with subscription model. The team had done some calculations on monthly usage to estimate how many people would be converted to paying customers. But there were still uncertainties.
The outcome was far better than expected and by Christmas it was clear that the number of users and time spent studying wasn’t greatly affected.
At Christmas eve, 24th of December, which is when it’s celebrated in Sweden, 385 medical students logged in to study. Here is a chart from Google Analytics describing when people logged on: