Full Idea
'Early to bed and early to rise' is a universalizable maxim, but, though it might be good advice, there is obviously no such obligation.
Gist of Idea
One can universalise good advice, but that doesn't make it an obligation
Source
James Gordon Finlayson (Habermas [2005], Ch.6:83)
Book Reference
Finlayson,James G.: 'Habermas' [OUP 2005], p.83
A Reaction
I take it that Kant's rule won't distinguish moral guidance from prudential guidance. Unfair, I think. I may be a lark, but when I universalise this maxim I see that it can't be willed as a universal rule, because we should tolerate the owls.