Circle Prefect is supplying monthly Terraria server hosting.
The service is such that each key provides one month of up-time which is renewed each billing cycle: per each month. Keys do not stack to provide more time. Each server instance acquired from a key lasts 30 days, and will refresh upon the automatic monthly subscription renewal.
World downloads, TShock plugins, and things such as REST API access can be requested at no extra cost, granted only the time it takes for support to respond.
Support is available at prefect | circleprefect | com (@ and . respectively). Located in the United States, response hours are likewise US-dependent.