http://privex3guvvasyer6pxz2fqcgy56auvw5egkir6ykwpptferdcb5toad.onion/articles/privex-bandwidth-policy-unmetered-fair-use
As you can see, burst bills can be very expensive, which is why we ask that customers on a Fair Use networking plan - avoid using more than 200mbps for more than 20 hrs per month, which would leave us 16 hrs buffer (or more - if they don't use the full 20) of leftover "free" traffic, which could be used by other customers.