I have checked in the Penguin and Oxford dictionaries of quotations and in
Brewer's, but have not found the reference. The owl is classically associated
with Minerva and I have seen the quotation used before; the implication is that
one sees better in hindsight (at the close of the day) than in the midst of
events. Please note that the owl is often used in military heraldry to denote
learning of an allegedly high order; the Canadian Land Forces Command and Staff
College, for example, uses an owl as the principal figure in its crest.

My colleagues and I suspect the quotation is from one of the English romantic
poets, perhaps Tennyson, who made other references to owls. I will keep
looking.

Harry Needham
Canadian War Museum