My worst mismatched tube was a 650c x 18-23 tube that had got into the wrong box at the shop, used in a 700x28 tyre.
With the diameter being too small, it fitted the rim like rim tape, so getting it inflated inside the tyre without being trapped under the bead was pretty difficult.
With the tube not having any proper use, it stayed in until the next puncture, which was only a couple of weeks, iirc.
Normally, I use the largest size available that will fit without folds, like SkipdiverJohn.
My experience is that stretched tubes go completely flat immediately on encountering anything sharp, but that unstretched tubes can leak fairly slowly, allowing you to delay changing tubes until you get home.
In one case, I had a half inch thorn through the tube for about 6 weeks, which only needed pumping every couple of days