I've learned the most from implementing papers. And being stuck. But me is me.

Since you mention SE, I'd choose a mini project in an area you love. The tooling you will learn along the way.

An hour a day is paradoxically not nearly enough, yet also a serious time investment of your day.

Maybe start by asking what exactly you want to learn? Applying ML to a practical problem, in user app? The math? The ideas?