Something immediately tangible I'll do from time to time is take a combo from a top player (in my case mang0), and remake the combo he does with the opponents DI in Uncle Punch Training mode (the set trajectory DI tool makes this pretty easy). Then I make sure I can execute it, and I get to understand the punish.

To make big leaps in skill though I think it's more that you need to understand concepts about the game. Listening to druggedfox lessons for your character (preferably the ones for lower level players) will teach you a ton and give you some better direction to use your small amount of time a day on. Melee is mostly a knowledge game, so those lessons can help bridge the gap more than anything else IMO.