So formal. So businesslike.
If my lover greeted me like this (or some variation on it) I’d have an instant knowledge that something was up. There’s something so distant, so full of niceties. She calls him lord. (Something she does in almost every subsequent sentence) and then also your honor. So she’s laid on two titles and additionally, she’s tacked on this “for this many a day” business which serves to heighten the formality. She’s talking like a LeBeau or an Osric. Can this possibly be the way she speaks to him normally? If so that’s a pretty dull relationship. (Or maybe it can be sexy, “Good my lord, would it please your honor to remove your shirt?”) It could be that she’s trying to signal to Hamlet that they are not alone. Unlikely. But a nice thought. Or it could be that this is how Polonius expects his daughter to speak to the Prince and so she has to put extra effort in, due to being watched. Or maybe this “my lord” business is just Ophelia business as usual.