[usr1106]

I always assumed that your free quota is proportional to the time you pay. Even the price is not the advertised fixed $3.5, you pay less in months with 30 days than in months with 31 days.

I have not checked my cost and usage reports every time I have some experimental instance for a shorter time, so I am not sure. Just from the general knowledge that AWS is permanently counting every fraction of a peanut. But as the submission shows, exceptions to the rule can exist.