Try gluing both the patch and tube and leaving them to dry overnight before putting the patch on the tube, just to show you can't wait too long.

I forgot a repair and left it for several days before putting the patch on the tube, and it held well.

It doesn't make it better to wait much too long, but I think it's important because it will free you to do something else instead of waiting, so the danger of waiting too little is much less. If you go do something for an hour after you glue your patch and tube but before you put them together, you will still have a good repair.