Well, first, I don't think you would forget you're going on vacation
And, second, you don't know what would happen between now and 10 days from now with your phone/your plans, etc. So the night before your trip, you SHOULD be checking to make sure your alarm is set anyway...and if the vacation is that important, make sure you set a REGULAR alarm clock, not just your phone. Suppose Murphy's Law goes into affect that night and your phone/tower craps out and doesn't auto-update the time and you don't wake up...If the vacation is that important, you need set a real alarm.
That said, were I entirely dependent on my phone for waking me up to my can't miss vacation, I would set an appt 2 days before to remind me to set my alarm for two days hence. (Since Alarm Clock v2 can set by day, you can set it up to 6 days in advance)...Then I would set another calendar event to 24 hours before to remind me to CHECK the Alarm that I set...
I wouldn't trust an alarm set 10 days from now. Too many things can happen to the phone...maybe FCs between now and then would screw up the alarm, etc. I'd be compelled to check the night before that the alarm was indeed set...So that's when I would set it in the first place.