they should be tighter than your tightest pair of walking shoes.

Well, then at about mile 60 your feet will be screaming for mercy.

your feet will swell with mileage. Loosen up your shoes a little at the first sign of discomfort.

DON'T wait until they really hurt! or it will be a long way home.

To that point, spend the money on the best fitting and quality shoes you can afford instead of the pedal that's 50 grams lighter.
If you are going to typically go for longer distances fit the shoes with some high quality Moreno wool hiking socks. (Smartwool, etc)