No, The first box that you initiated the change on will change pattern first, then after the other box plays the same pattern it was already playing “again” on more time it will finally change to the next pattern and both boxes will then be on the same pattern at that time. This is if you use the built in “Send Program Change” and “Receive Program Change” functionality built into the boxes.
If you manually send a program change some other way “before” the end of the pattern, it changes when it’s supposed to. Otherwise, using the method I described here (the built in method) the patterns will not change at the same time but will come into “sync” after another loop of the previous pattern.
This behavior does not happen when using “Send Program Change” / “Receive Program Change” when the Octatrack is the receiver. Octatrack pattern will always be on the same Bank and Pattern number that the DT/DN is on whenever you initiate a pattern/bank change starting with the DT/DN keeping the patterns/banks in lock sync with each other at all times.