We post a time by which protests must be in, and then say that hearings will be scheduled. All Parties are then informed.

Anthony, WS SI Guide 17.3 provides the following sample wording  Notices will be posted no later than 30 minutes after the protest time limit to inform competitors of hearings in which they are parties or named as witnesses. 

The function of this is to facilitate the prompt hearing of protests after racing on each day.  It would be unusual to specify a time in such a SI that was after the last day of a regatta.

If  the NOR/SI requires a hearing schedule to be posted by a certain time, and only 'TBA' or 'to be discussed' is posted, then I think that this may be an improper omission by the protest committee, but I can't see how, if the reason for not stating a specific time is the failure of a boat to agree on a time, there is not fault of a boat's own, and thus there is no entitlement to redress.

Conceivably a third party boat might request redress, claiming that uncertainty about the hearings made her score worse, but that would be a pretty tenuous claim.

I've got to say, however that if the OA/RC put this provision in their NOR/SI, the protest committee shouldn't get drawn into haggling with boats about the schedule:  just select a reasonable time and publish the schedule.

We need to cover the eventuality of a redress case. If you posted that a case is happening with the 2 parties listed, then the „no fault of their own“ part is activated. They need to give proper reasons why they couldn’t be at the hearing, despite them being on the list.
Nonetheless after posting the time and place for the hearing you should factor in a discovery timeframe unless the parties are directly informed.

So posting a preliminary hearing schedule without times is most of the times enough to prevent a procedural error. And it is a good service to the competitors if it is posted as early as possible. 

There are instances when the hearing time is indeterminate.

For example, here in Detroit, much of the summer week-night racing hosted by various clubs ends after dark. The protest time limit is 12 AM. Anyone wishing to file a protest does so electronically (photo of paper form or PDF, emailed to a published email address) by that time. The email is automatically forwarded to several people, including the Chief Judge of the Detroit River Yacht-Racing Association.  The next day, the CJ notifies the protestee and starts the process of assembling a jury and determining a mutually agreeable time for everyone to meet - usually within a couple of days, but it has taken as much as a week.

This is all covered in the standard SIs that the clubs use in this area.

Matt, I'll bet the  NOR/SI does not require a hearing schedule to be posted by a certain time.

That was the condition in the OP, and the cause of the problem, whatever it may be.