Hi Ben, I can only refer you to the marklin digital youtube webinar on advanced event programming. I am a novice myself. It looks like you want three events, two with long delays.
You may need more than one contact or block area. Advanced events can include an "if, or a "then" condition in order for the event's and sequences to run correctly.

Assuming you have a circuit track on the shared track and contact tracks on both unshared tracks this is how I would do it. Loco A is sitting on one unsshared track, when loco B hits the circuit track it triggers an If event activating the switches so that the empty shared track is open. When it hits the contact track an event is triggered either sending it around again or stopping it, activating the switches for the other track and then sending the other loco around. Repeat as desired.

Also Ben, a condition is usually followed by an "action" first in an advanced event.

Unfortunately the event is triggered each time the loco makes contact. You might try a ridiculously long delay but not sure if it will work.

Assuming your two trains after passing onto the shared track continue on a loop and returns to their starting points in front of discussed turnout:
Define in CS3 a virtual contact as if for contact track connected to s88 device, however you dont need the s88, adress or contact track. The virtual contact will be as a block name for the shared track. In your events you can define this as occupied(yellow) or free(grey) only way to change status is in event(or if you drag its symbol into your track plan and press on it)
Now. Event for first train: drag the virtual contact into the command line, set it to free(grey) and delay until virtual contact is grey(free) this will halt this event until contact is set to grey. Commands to follow in this event is to set train moving etc. then you set the feedbac contact the said train into the event and set it delay/wait until triggered. Next command of course to stop train. Then you insert the virtual contact again, and this time set it to occupied(yellow) alternatively you can send the train on anorher tour around the loop prior to the virtual contact is set yellow.
Then; event for the other train: more or less the same but to wait until virtual contact is yellow before set on route and when triggering contact prior to turnout either set for anorher round or stop train and set virtual contact to grey.
When starting the two events manually the train waiting for the color that is already in the virtual contact will start. The other wait. Hope this was understandable. It is also possible to make an event and drag the event for train a several times into this event. Similar for train b. Startin these events will make the sequence repeat.
Regards
Thor Inge