Which time zone does iMessage use for delayed sending?

When selecting to time to delay the sending of an imessage, does one pick the time where the message is being sent, or the time where the sender is? To send a message to Guam, it would be easiest to pick a time that is local for the receiver in Guam, rather than calculating when that time is while I'm in Tucson, AZ? I've searched for a proper answer and can't find one. Any help or advice on this would be greatly appreciated.