Starting a solid study schedule?

"I know endgame study is super important but how should I begin going into deeper opening study yet?"
So you know, but you want to do the opposite...

Many players became quite good although they read „My System“ - a nice historical work but there are tens of thousands better books at hand today.

Some wrong advice here. Most are good hints.

First part: Don't only look at chess, look at your strength(!) and weaknesses. Building up good habits. 15 min 5 days a week is better than once two hours. 1 hour daily is too much for most of us.

You will only stick to topics you like. If you like endings, start with them. If you like tactics start with tactics.

Read a little about thinking in chess. Adopt it to your situation and fondness. J. Tisdall - Improve your chess now - is underrated imo. Aagaard - Excelling at chess has some good hints. J. Rowson is educated in cognitive sciences and his 2nd book is excellent. Most prefer his 1st book, which is worth more than one look too. If books aren't your choice, go to the Quality Chess site. There is a section in the blog with the training hints of Aagaard. Start reading them from the oldest entry, from time to time. Adopt it to your situation.

Analyzing your own games! What are your mistakes? Build up categories and look at the notes from time to time. This will show you what to do and give some motivation.

A buddy to discuss is helpful. A trainer should be strong! Strong is beyond 25xx. I know this advice will be attacked. A trainer on GM level gives sees faster and knows more, having a higher probability of giving good advice. After a game of mine I saw my opponent discussing it with his trainer, IM and 2350 FIDE about, and his hints to the KIA were correct in one system. But he IM told they were correct in all branches of the KIA, which was wrong. That's only an example of the general principle behind my reasoning.

Summary:
1.Build up good habits.
2.Thinking about thinking, general and special (how to find a move, etc.).
3.Read.
4.Analyze your games and collect your mistakes.
5.Socialize.

Have fun!

According to this, rather dated, distribution chart you are already significantly better than the vast majority of USCF rated players, let alone unrated players. (http://www.uschess.org/archive/ratings/ratedist.php)

An almost "Class A" player, working only from principles and little or no opening theory.
In other words, a natural.

A friend of mine - a young Indian chess prodigy named Ajay Karthikeyan - recently obtained his FM title.
He confirmed to me that he never spent any serious time with opening study before reaching 2000 FIDE. (Perhaps a bit less or more but I don't remember the precise rating as of this writing)

When I checked out his ratings graph over on FIDE's website, I noticed a stupendous ratings boost (+500 points) in less than a year: he went from 1770 to 2260 between Jan. 2017 and Sept. 2017! https://ratings.fide.com/id.phtml?event=35011685

When I queried him as to how he achieved this momentous leap, he answered: I practiced a lot of tactics and played some tournaments in Spain.

Now, even though I don't think he was being entirely facetious about the Spain part, I am 100% convinced about the tactics part. Just this morning he posted a comment on my profile page over on Chessable to the effect he was going back to tactics study, finding opening study too boring, ha, ha. Feel free to check out my profile page there to confirm. https://www.chessable.com/profile/PixelatedParcel/

Me? I am an old coot (56) who never studied the game and was never more than a casual player.
As my ambitions are modest, I'm betting a firm grasp of opening principles and chess fundamentals will last me a long, long time.

Almost all of my study-time is spent on Chessable (which I wholeheartedly recommend to you, if you don't know the site) and has almost exclusively been devoted to endgame study and the study of about 25 games of Paul Morphy. (I have studied other stuff, obviously, but that has been my "bread and butter".)

Now, feeling I am grounded in at least basic endgame theory and practice, I am switching my focus to tactics with a particular emphasis on checkmating patterns which exist in a surprisingly large variety I have recently discovered to my delight.

I believe that the way to improve is through solving tactics(OTB) and if you can pick up 3-5 tactical motifs, learn the patterns and then solve problems by creating a problem set based on the ones learnt ( I see ChessTempo) being good for those and solve them regularly OTB( helps in visualization and calculation which is a must for any Chess improvement). Once a set is completed, pick additional motifs and repeat the process.