Hi frymeapples,
There's no subscription, you pay once and get to use it forever, with free updates as well.
Both versions, macOS and Windows, are included in the price. You can run them on any number of computers you have.
The best way to test how long it takes is to simply test with the free demo. You can download it for macOS and Windows. The demo basically does the same as the full version, but the output is changed once it finishes, every other line of the transcription is changed to a demo sentence.