palaceben The windows should be fine and will get populated for the today/next day at around 16:15, so your 19:30-08:30 should be pre populated then, provided you have not already selected a slot within that window, sat at 20:00, before we run the schedule population at 16:15, in which case we don't touch it, and assume you are manually picking slots, as you've already done.
Does that make sense?