Schubert's 'Adagio' in D-flat major, D.505, is a beautifully crafted lyrical movement with a poignant melody and rich harmonic language.
Mastering the nuanced pedaling and subtle rubato is crucial for capturing the piece's expressive ebb and flow.
Adagio in D-flat major (D.505) 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 Adagio in D-flat major (D.505) lasts about 4 minutes.
Adagio in D-flat major (D.505) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.