Here's a practice routine I have. I set the timer for 10 minutes, and practice one tune. I have a list of 9 tunes and I play all of them Then for another 10 minutes I play another, random tune, a different one every day. This is 100 minutes. I can also halve it and have a 50 minute day. It doesn't have to be all at once, I can return to the piano throughout the day. What is important is that concentration must remain on the same tune for the entire five or ten minutes.
The tunes vary in difficulty and also in how well I know them. I figure that I could be doing some combination of three types of learning: learning (for the first time), solidifying, or deepening knowledge. Thus it doesn't matter where on the spectrum a given tune is. If I don't know it well, then I am learning it; if I do, then I am deepening my knowledge of it. I have to be careful that I don't get stuck playing something the same way every time, solidifying when I should be deepening instead.
5 or 10 minutes is enough to learn, better, one part of a tune, to develop some new improv ideas about it, or to solidify some parts of it. If I don't know the tune at all, it is enough time to play through the melody several times, or to get down a four-bar phrase with the chords.
If this works correctly, then I will have repertory of 9 standards. I could modify the routine by subbing out a tune for another one. The tenth tune is actually the most important part of this, because that allows me to avoid boredom, practice sight-reading, and to gradually expand my knowledge.
The tunes are these
One note samba
Rhythm changes in Bb
All of me
All the things you are