Yeah, it's tricky. It took me a bit to figure out how the mechanics work.
It doesn't add the time you select first. It just adds a default time no matter the selected day of the week and time. After you add a default entry, you must click the entry as many times as needed until the day & hours in the top editable boxes are linked to the entry. You know they're linked when by editing the day or hours, the entry's day/hours change instantly. If they don't change instantly, they're not linked and you must click again the entry until they are (day/hours in the editable boxes become the same as the entry's).