I believe that, as a matter of course, vacations ought to be 3 weeks long.
To be clear, mine never have been, but I got the idea from a dear friend years and years ago. Her reasoning was that the first week you're busy decompressing and the last week you're thinking about returning to reality, so really it's the middle week when you can be fully present on vacation.
I've dreamed of it ever since, and I'm determined that one day I'll try it for myself. In the meantime the thought of it helps me to remember to be right here where I am for the time I'm here.