Date/time selection errors are not discoverable by screen readers

### Expected Behaviour
There should be some kind of feedback mechanism when a date is not considered valid.

### Actual Behaviour
The selector indicates there's a problem with the date selected, but there's no tip as to what the error is-the time seems valid to the user. The error prevents the request's submission. Visually impaired users receive no indication there is an error. The modal appears to require a 3 day lead for scheduling sessions without stating so. Screenshot attached.

### Reproduce Scenario (including but not limited to)

#### Steps to Reproduce

1. Navigate to:
2. Click on Request expert session button
3. Turn on the system's screen reader utility
4. Tab and fill out form to the first date time selector control
5. Set the first date time selector to 1 day in advance

#### Platform and Version

#### Sample Code that illustrates the problem

#### Logs taken while reproducing problem