i'd split it up into segments: work on the tunes you already have down (10mins), then work on tunes you can't play (10 MINS), then work on, if you can't sight read, reading music notation or if you can sight read work on composing or something. i typically do two or three half hour sessions a day cus i think that the mind can only absorb so much much in an amount of time. my sessions include 10 minutes of bach 10 minutes of soloing to the music in my head and then 10 minutes of trying to write stuff. much of that is disgustingly awful but it helps in the long run with improvising and just having cool songs to play that you can call your own.
If you don't go when you want to go, when you do go, you'll find you've gone