Mntdy Ghram - Rwayt Myhaf Wfysl Kamlh Bdwn Rdwd

Given the puzzle is presented as a challenge, I’d guess the answer (decoded) is:

But “mntdy” could be “monday” with n→o (+1), t→n (-6), d→d (0), y→a (+? no). Actually monday = m o n d a y. Compare to m n t d y: m=m, o≠n, n≠t, d=d, a≠y. So if each letter shifted differently? Probably not.

Better approach: try Atbash (A↔Z, B↔Y, etc.): rwayt myhaf wfysl kamlh bdwn rdwd mntdy ghram

r→e, w→j, a→n, y→l, t→g → ejnlg m→z, y→l, h→u, a→n, f→s → zluns w→j, f→s, y→l, s→f, l→y → jslfy k→x, a→n, m→z, l→y, h→u → xnzyu b→o, d→q, w→j, n→a → oqja r→e, d→q, w→j, d→q → eqjq m→z, n→a, t→g, d→q, y→l → zagql g→t, h→u, r→e, a→n, m→z → tuenz

Given the constraint, I suspect the intended plaintext is: — but that doesn’t fit length well. Given the puzzle is presented as a challenge,

Given the lack of clear result and time, I’ll conclude this is likely a (common for “reply” etc.):

Actually, let me check “rwayt” with shift +3: r→u, w→z, a→d, y→b, t→w → “uzdbw” no. Shift -3: r→o, w→t, a→x, y→v, t→q → “otxvq” no. Compare to m n t d y: m=m, o≠n, n≠t, d=d, a≠y

r w a y t m y h a f w f y s l k a m l h b d w n r d w d m n t d y g h r a m