Alkan's Preludes are a monumental and demanding cycle, exploring a vast range of keys and expressive possibilities. They are characterized by their virtuosic demands and profound emotional depth.
Mastering the extreme technical demands, including rapid octave passages, complex rhythmic figures, and wide leaps, requires exceptional dedication.
25 Preludes (Op.31) is rated Henle level 7 of 9 — late advanced repertoire, roughly ABRSM grade 8 and above. In the RCM system it corresponds to about level 9.
You should be comfortable at Henle level 7 — meaning you can already play level 6–7 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of 25 Preludes (Op.31) lasts about 50 minutes.
25 Preludes (Op.31) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.