If they're pinching your toes or heel right now, that problem is almost never going to improve on its own. I made that mistake years ago with some similar loafers - I thought they'd stretch out naturally and ended up storing them in the closet because they were never actually comfortable. Leather does stretch, but the stretching is very limited and mainly happens in the width of the vamp and the sides, not in the toe area or the overall length of the shoe.
What does help is wearing them around the house for short periods over a week or two to see if the overall fit improves. This is different from just waiting passively - this way you feel for yourself if they start to give in specific spots or if they just hurt the same. If after a week of wearing them at home they still hurt when you have them on, then you probably needed a bigger size. With loafers it's especially important because the leather in the vamp area and the back tends to hold its shape pretty well.
My advice would be to go to the shoe store right now and try the next size up if you can. Sometimes you regret it after you get home and it's better to sort that out while you still have the chance. If the shoe store has an exchange policy, do it now rather than wait two weeks and figure out it didn't work.