What is the default weapon switching time?

How can I calculate with the help of the numbers in the TF2 wiki how long does it take, in seconds, for any class to:

1. Fire with one gun (start stopwatch)
2. Switch to another weapon
3. Fire with the second gun (stop stopwatch)

The one specific scenario I need help with is the minimum time between sapping a building and starting shooting it with your gun.

Solution 1:

According to an interesting forum post describing the advantage of the degreaser, the default switch time is 0.67 seconds.

As far as I know only the Degreaser (65% faster, 0.67(1-0.65) = 0.2345 seconds) and Reserve Shooter (15% faster, 0.67(1-0.15) = 0.5695 seconds) can affect this, besides the weapon-specific limitations as mentioned in Toomai's answer. Also of course the Half-Zatoichi is 'honorbound' and has a switch time as long as it takes you to get a kill!

Solution 2:

Here is how I would do it:

• Use sv_cheats 1 and host_timescale 0.1 so that time advnaces at 0.1x speed. This will increase the accuracy of your measurement by a factor of 10. (Maybe 10's a bit much, but it's what I would do since dividing the measurement by 10 is trivial.)
• Set up an enemy right in front of you.
• Start the clock and switch to a bullet-based weapon.
• Hold down the shoot button during the switch and stop the clock when the weapon does damage (not when you hear/see it fire, which might be slightly out of sync with the actual damage dealing).

Note that you don't need to fire a weapon to start the clock here; your starting point is when you press the "switch to another weapon" button. This is because you never have to wait for something before you can switch to something else, with the exception of Heavy primaries needing to spin down or hauling buildings.

Once you've done this a few times with regular weapons you can go from Degreaser to Shotgun to see if that measurement matches up with the expected value.

I won't help you with the sap-and-shoot measurement because Spies that do that are jerks. :P (Seriously though: Since there's no delay before you can switch regardless of the weapon, the measurement won't be different than anything else.)