This depends on how regularly your Dojo runs and on your specific role in the Dojo. Usually, mentors attend their Dojo’s meetings and help out for a couple of hours, whether that’s weekly, twice a month, or monthly. On average, Dojo sessions run for around 1–2 hours.
If you are preparing projects or content for your Dojo's next session, this may require additional time. Typically, a champion will contribute more time than other volunteers, as they are usually responsible for most of the planning. Other tasks should be delegated as evenly as possible amongst volunteers to ensure everyone is contributing a fair amount of time.