You use hours by running a private session. When you press Start, the first block of minutes is charged to your balance at once: at least 15 minutes, or all of your balance if it holds less. Preparing the session is free: if it never becomes ready, for any reason, including a cancel, all of those minutes go back.
From the moment the session is ready, it is billed per minute, and each started minute counts in full. Every session that becomes ready is billed at least 15 minutes, or all of a smaller balance, even if you end it sooner. While it runs, the next block of minutes is charged shortly before the current one is used up, as long as your balance holds minutes.
A session keeps running until you end it, your hours run out, or no request reaches it for 20 minutes. Closing the app or your browser does not end it. If you turn on Keep my session running in Settings, it does not end for lack of requests, and you pay for all the time it runs. A session schedule you set in Settings starts and ends sessions for you, and these terms apply to them as well.
When a session ends, the charged minutes it did not use go back to your balance. When your hours run out, the session stops taking new requests; answers already being written can finish.
If a problem on our side interrupts a session, we move it to another server automatically, and the time it spends preparing again is not billed. If we cannot move it, the session ends and every minute you could not use goes back to your balance, even within the minimum.