How am I billed for my instance?
All reserved resources (allocated instances, storage, floating IPs etc...) on your account are billed hourly up to the monthly rate cap. The hourly rate is determined by dividing the monthly rate by 672 hours (28 days). If your server is online for more than 672 hours in a calendar month, you will only be billed the monthly rate. Accumulated charges are invoiced to your account once a month.