to warm up, i use chords (5 notes, diminished chords - made from minor3rds), played 1+4 (notes), 2+3, 3+2, 4+1. after that, i play chopin etudes at half tempo and go progressive towards actual tempo. personally, i prefer op. 10 no. 1, 2, 4, 5, 8 and 12; also op. 25 no. 6 and 8. doesn't take more than 20-30 min (timing depends upon needs), and works pretty good.