My opinion differs from the majority of the above, only I do agree that 1 day's early results aren't enough of a time frame to take action from. If you had a day's early games in 1 particular league go all Under (or Over), and that was on top of that particular league's games having gone mostly the same way total result wise the previous 5-6 days (ie, come out ahead of), then I'd look at the most obvious opposite result games within those late games and as long as Ump & weather conditions gave a green light, I'd go ahead and back it with confidence.
In my experience of recording results, unders dont occur 100,000 times out of 100,000, and this isn't a roulette wheel. The same pitcher isn't being wheeled out every day, the same batters aren't physiologically in the same space everyday, the same weather conditions don't apply every day. Those variables guarantee that lengthy ocurrences of either total result for a particular league as a totality never last for more than 5-6 days before the opposite total result at least ties a day (AL 3-3-1, NL 4-4). So if you've had 5-6 days of Unders winning in a particular league every day, then Under comes out on top for 3-4 early games the next day, feel safe an Over correction of sorts will start to make itself felt in those coming night games and if they don't, then the next day is a green light for said results. The immediate observation that these games have no connection to one another so there's no reason that should be, has logic on it's side. The way things actually pan out in real time runs counter to that logic. My basketball trend thread I've kept for 6 seasons manifestly represents the fact. I don't keep such a thread for baseball because there are 2 different leagues, this is a ml based sport and the fact there are so many more games played. All that means the arcs of results are much less even in immediate terms than what they are in the NBA, so less amenable to being made use of with any certainty. It's just as easy to not do the intensive work of recording all results, and more quickly noting "freehand" when 5-6 days of 1 result have predominated (which is something I actually do when I'm fully focused on the mlb, but I'm not currently).