Why linked
Q&A heading names “Chronobreak”: go to paragraph
Chronobreak and chain order
What's up with the reminder text on Chronobreak? Do I get to choose the order?
You get to choose the order if you own all of the units being banished. If you control some number of units that you don't own and banish those units as well, the units you banish will be placed on the chain starting with units owned by the current turn player and then proceeding in turn order.
Items cannot be placed on the chain simultaneously for any reason. If chain items would be played simultaneously, their controller chooses the order they go on the chain. If multiple players would add items to the chain simultaneously, they place their items on the chain in turn order instead, starting with the current turn player. In the case of Chronobreak, each player chooses the order of their own units being played to the chain (this is what the reminder text is referring to), but each player plays their units to the chain in turn order, starting with the current turn player.
Example: You control five total units, two of which are owned by your opponent. You play Chronobreak, choosing all five units. You banish them, then for each, their owner plays them to the chain as pending items. You're the current turn player, so you play your three units first in the order of your choice, then your opponent plays their two units in the order of their choice. Pending chain items are finalized from oldest to newest and units resolve as soon as they're finalized. Thus, we go up the chain starting with the first unit you played to the chain, finalizing and resolving all of the pending units on the chain until there are no more units on the chain. Then we finalize any play effects of those units in the order they triggered. Finally, players can react to the most recent item on the chain. If they don't, that item resolves, and we repeat the process until all items on the chain have resolved.
Relevant rules: 303.2.a.