Neither Hotmail nor Google support such functionality by default, though it would still be possible if you found an e-mail client (or extension for one) that supported such functionality. The only requirement would be for you to leave your computer on and connected to the Internet at the time you wish the e-mail to be sent. Off hand I cannot name an e-mail client that supports that, though. Perhaps there is a Mozilla Thunderbird (not compatible with Hotmail by default) extension?