Regarding levels, if you heard me play, you'd know what level I was at. If you heard me sight reading, chances are good that you'd recover
This is developing into an interesting thread.
The OP has already qualified his definition of advanced and he's wanting to know how far he can go with a diligent practise regime.
There's a lot of myths out there that late starters won't make it on piano and rubbish like not teaching old dogs new tricks. It's very reasonable that some one would want to know and it's nice to dispense a little truth.
Bach's Well Tempered Clavier and the sonatas of Mozart and Beethoven, the mightiest aside, are all about grade eight (ABRSM) and that's within the realm of anyone starting from scratch at any age. People take up the piano in their retirement, or return to it, and many make grade 8 within ten years.
To the OP, it's not the time you spend that will determine your progress but what you do with it.
One of the main things is to spend more time trying to play what you can't yet and less time playing what you already can.
Read something new every day. I wouldn't want to put a time on it. My sight reading varies day by day from a couple of difficult lines to a couple of easy pages. It varies from keeping up with a drum machine at tempo, wrong and missing notes aplenty, which gradually get sorted over a few repeats, to a slow and meticulous exploration of the music.
I have taken to the Australian/Hal Leonard initiative of forty pieces a year and I pick a new piece more or less every week. Some pieces are done in a couple of days, the odd one might take another week. They're easy pieces, mind, that I CAN do in a week to a reasonable level of competence.
Memorise something new every day. It doesn't have to be more than few bars or even just a few notes. But doing it every day makes it easier over time.
Learn new pieces but don't neglect past repertoire. I believe it's only the pieces that mature over many years that enable the push to higher technical levels.
Whether you want to target technical skills for their own sake or develop the techniques you need from and for your repertory pieces is personal (unless you're doing exams). I think I'd go nuts if I had to do 20 minutes a day on scales and arpeggios but if they are part of a sonata I'm happy to spend 30 minutes a day for a few weeks. I never spent a lot of time on scales and arpeggios but I've devoted hours to the scale passages in the recapitulation of Mozart's K.545, for example.
Bob's already pointed the way to Bernhard and Chang. Add Graham Fitch and Dr Brent Hugh to the mix and there really isn't much more to learn about how to go about practising. Try stuff, record what you've done. Then try something else. If it works add it in. If it doesn't work you've learnt something about yourself.