When you click into the date text box, a calendar will pop up for you to select the date AND the time.
1. Select the date on the calendar you wish to close OLC.
2. You may either double click inside the hour, minute, AM/PM setting(s) or use the up/down arrows to change the hour (which will also update AM/PM when appropriate
3. Make sure the data you've selected on the calendar/clock pop-up MATCHES what is in the Finish deadline, or your updates will not save.