It took the customer almost 6 months to exceed the free plan quota, but eventually they did upgrade. We're now thinking how can we shrink the trial time, but offer more value from the start at the same time. Options are: offer a short trial, and then disable an account when it ends vs. give a short trial, and then disable some premium features at the end of it. Second option seems preferable, the only problem is that we don't have any premium features yet :)