The time you pick is the time your video goes live. Choose your posting days and a time of day, on the hour or the half hour, in the timezone you set, and each post publishes to YouTube at that moment.
The work starts before then. Chillframe begins rendering up to two hours ahead so the video is ready in time, and that post's usage is taken when the render starts, not when it publishes. If the Series is set to Manual approval, the finished video waits for you instead of going out at the slot.
A slot that passes while the Series can't post is skipped, and the Series aims for the next one. You won't come back to a pile of late posts landing on your channel at once.
To change the rhythm, open the Series, go to the Schedule tab and press Edit posting window. You can change the Time and the Timezone there, and saving reschedules the upcoming slots straight away. Posting days aren't in that dialog. To run on different days, make a new Series, or ask a connected agent to change them for you.
The reasons a slot gets skipped, and the fix for each, are in Why a scheduled post was skipped.