Between October 2020 - January 2021, it was actually a bit easy to figure out when a program would be fed. For example, say a new episode of "Finding Your Roots" airs on a Tuesday. PBS would feed that episode on HD03 on Sunday, two days before it aired. PBS usually did this with new episodes of programming, usually fed one to four days in advance. For example, "Independent Lens" would be fed on Friday and usually aired on Tuesday or Thursday, "Nature" and "NOVA" would be fed on Tuesday and would air on Wednesday, "Masterpiece would be fed on Friday and air on Sunday, "POV" would be fed on Friday and air on Monday or Tuesday (not sure which), and so on.
American Public Television feeds films as part of their feature film package during the last week of the month, usually starting at 12:00pm ET for consecutive days. If they have four films to feed, they would most likely feed them at 12:00pm ET Monday through Thursday, for example. However, last month, they fed two films in two days, so two films per day. APT only has two films to feed this month, so the feeds may start sometime this week, maybe even today. If that's something that might interest you, tune into HD03 at around 12:00pm ET through the week, since I'm not sure what day they'll be fed.