I think this is the first part of the answer you seek.
CHAIN AFTER controls when chained patterns will start to play. The default mode is PAT.LEN. When a pattern is playing and a new pattern is selected, the pattern currently playing will play to its end before the new pattern starts playing. If PER TRACK scale mode is active and a very long, or infinite, master length setting is used it might be more convenient to initiate a new pattern after the active pattern has played a certain amount of steps. Set the amount of steps using the LEVEL encoder. This setting affects all patterns in a project, but can be overridden on a per pattern basis in the PATTERN SETTINGS menu. There the USE PRJ SET. setting can be unchecked, allowing for a unique chaining behavior for the chosen pattern. Read more about the PER TRACK mode and the master length setting in section “SCALE SETUP” on page 92. Read more about the PATTERN SETTINGS menu on page 89.
Thank you. It’s close, but not quite the way Spark (as an example, I think Maschine too) does it - there you have free rein to switch a pattern on-the-fly at any step. I love this method for jamming. Maybe the OT has other ways to achieve the same result - I’m on the fence pre-purchase!