Welcome back! So glad to hear you're getting back in the saddle and that things so far are going well.
Sometimes when I feel like i'm overtraining or getting nowhere or my horse is getting ring sour or acting out, I just go out to the ring to ride with no time constraints - at all. I may ride for an hour, or three, depending on what my horse needs. It's mostly walking, a little trot and some transitions, and at the end a tiny bit of canter. Lots of walk trot transitions and lots of stretching. And I just listen to my horse tell me when my back is hollow, or i'm weighting the right seat bone more than the left, or if i've started hovering bc i'm protecting my knee injuries, and so on.
I find that simple goals on days like that are both far more challenging and far more rewarding than going out with a time frame and a concrete plan. Today we went out there with the goal of warming up at the walk, and then doing some transitions and the final goal was to trot the entire ring consistently on the bit, engaged, relaxed, soft and balanced, including one circle. It was a lot harder than it sounds when you're paying attention to not just your horse, but fine tuned into yourself and your own aids and balance and body.
To keep from getting bored or repetitive, i'd add leg to work on mini-leg yields or shoulder ins here and there, i'd work on in-gait transitions from longer to shorter strides and faster and slower. And everything I did with as little rein pressure and as soft of a contact as possible.
We ended with almost no need to canter, and the canter we got was slower and more balanced - from the halt! - than my horse has been in well, maybe ever. And leg yields on both canter leads! He's a jumper and we both tend to get so amped up that it's easy to lose sight of the focus on the little things, and making sure that we're still connected and working as a team.
Not only was it a good, calm, quiet challenge, it did a great job of getting him more fit and balanced and looser - all which will help our performance in the jumper ring :)
Good luck - and above all enjoy more than just the riding, but the connection and the partnership!