Joachim Raff's '12 Romances en forme d'études' Op.8 are technically demanding pieces that blend the lyrical character of romances with the pedagogical purpose of etudes.
Developing finger dexterity and control of rapid passages while maintaining a beautiful tone is the key challenge.
12 Romances en forme d'études (Op.8) is rated Henle level 6 of 9 — advanced repertoire, roughly ABRSM grades 7–8. In the RCM system it corresponds to about level 9.
You should be comfortable at Henle level 6 — meaning you can already play level 5–6 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 12 Romances en forme d'études (Op.8) lasts about 40 minutes.
12 Romances en forme d'études (Op.8) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.