Well, though all these puzzles book are fine, I think it doesn't replace looking at some master games to get a feel for the "flow" of the game. I understand 30' is a bit short, but what you could do is to go through the game during the first session, no trying to understand everything, but simply jotting down which moves looked "weird".
Then, on the following day, you go through the game again, and try to understand those weird moves. Even if you don't understand everything, this routine is bound to be very beneficial over time, and spending like 1hr on a good annotated game should already be good enough to learn a lot.
Quite some time ago I've decided that my chess training should combine 4 elements:
- tactics
- endgames
- practical play (CC, OTB, live)
- all the rest
"All the rest" was planned as study of master games mainly. And here I fail regularly. The problem is that due to constraints of family life and work I do chess in chunks of 15-30 minutes. That's enough to solve few tactical exercises, study 1-2 endgames, play a rapid live game or make few moves in CC. But that's never enough to go through a master game even once.
So I will either go through a game and comments very fast, then it's rather shallow and I feel like learning nothing. Otherwise I have to split it into several chunks where I do nothing else but only study this particular game because I need like 2-3 hours to really understand one game in depth. And I never succeed in this - I'd start one game and then it's dragging and I forget what was going on, loose focus and eventually drop it.
I've discovered recently that positional exercises can be a nice alternative. You find them in books like "Can You Be a Positional Chess Genius" by Dunnington, "The Chess Cafe Puzzle Book 2" by Muller or "Test Your Positional Play" by Bellin and Ponzetto.
Here you are usually presented with one critical position from master game. You have to analyze positional factors, make a plan and implement it. Playing it against a computer is quite interesting too. One exercise can be completed in 15-20 minutes which fits well into my time constraints.
I will appreciate your comments and ideas.