It depends on the cane, not the time of day. Only crook top canes are specifically permitted. Flat top, knob-headed and other canes with a "decorative" aspect may be considered to be potential weapons, at the discretion of the airline personnel, while crook top canes are viewed as less threatening.
That's how things stand at present. Obviously, ANY sort of stick can be a formidable impact weapon. The canes from
www.canemasters.com fill the bill nicely. DO NOT attempt to carry on any sort of sword cane or other hollow, compartment-type cane, as it WILL be X-rayed.
One tip: Don't sit in an exit row if you carry a cane on board, or your "abilities" may be called into question, either to assist passengers exiting the plane via that row, or regarding your "need" for the cane (even though it's nobody's business).
To date, I've had no need to produce evidence of disability on boarding a plane with my Canemasters Professor cane.