I think he is meaning something else like: The signed message "xxxx and address xxxx and signature xxxx" has been signed on Tuesday 21 July 2015. If i understand his question
well theere is no "date" field in a signed message, all there is are an address, message, and signature. if the message is dated the date would be included in the message, and the signature would be different compared to is the date was not included in the message as the message would be different. if youre asking if the date the message was signed could be verified or seen with the date not being explicitly stated in the message, no, i dont believe there is a way to do that.