Our accessibility testers said that the 'new event' calendar form is not of acceptable quality.
In the longer term this should be replaced with an mform, but for the time being, I have done a patch with some changes (more labels) to this form, and added hidden labels ('Day', 'Hour', etc) to the old-style date and time selectors that are used. These hidden labels are the same as the ones used in mform date/time selectors.
This change is not supposed to make any difference for sighted users.
I'd like to put this into MOODLE_19... (Patch is for OU moodle but applies straight away to MOODLE_19).