If properly motivated I can either fix a flat or replace the tube in about 5 minutes; it takes me about the same time to do either.

I tend to be a bit different the rest of you here because I would rather try to fix the tube first rather then replace the tube first. The reason for that is because if I have a couple of flats on the same ride I don't want to deal with 2 bad tubes. Also you have to spend time to take all the air out of the old tube before you can stow it in your seat bag. Plus I can usually find the leak within a matter of a few seconds anyways.

The fastest way to repair a flat with folding tires is to remove only half the bead on one side with the hole in the middle, then pull about 1/4th of the tube out again with the hole in the middle. Then simply buff, apply a glueless patch which is faster then the glue type and last just as long no matter what anyone tells you, then get the offender out of the tire, and restuff the tube and seat the tire. When replacing a tube you can use the same procedure accept you remove the entire side of a tire.

There is a tool called the Quik Stik that makes ripping the beads off a rim a snap and fast.

Steel beaded tires or non folding tires on road bikes may require that you remove one side of the tire because their sidewalls tend to be stiffer.

I mostly road bike and I now use Specialized All Condition S Works (700x25) tires with Specialized Turbo racing tubes but I am considering trying latex tubes again.