You would only change builds when passing a production state. A cycle change would be basically a production build has been released that is newer that the previous beta or nightly builds.
ex.
Update to nightly > Switch to beta> You'll continue to get nightlies > Next cycle change (Production build released) > if your settings are set to Production you only receive the next Production build. If you set your settings (back in step 2) to Beta you should receive the next Beta when one is available. You'll continue to receive Betas. If your settings remained on Nightly in step 2 you'll receive the next available Nightly when available. You'll continue to receive Nightlies.
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Think of it as a toll road or rail system. Once you get in the carpool lane/ on the tracks you can't exit till the designated area. That would be while the next Production build is on your device. I always recommend setting your desired channel before the next release to ensure you do not miss the lane change area. Else you may need to continue on the ride again.
It is possible to make the change manually should you wish or need to do so. There are a few steps to take if you want to get off the train before the next train station.