How do i get the wait time and pause/unpause an animation while a key is being held?

Check this out for the info on Keyboard input: http://wiki.roblox.com/index.php?title=Keyboard_input

As for the pausing and unpausing, I can't be very much help. But I can show you how to fire a function when a key is being held, and get the wait time.

Here is the basic structure for getting the keyboard input:

function onKeyPress(inputObject, gameProcessedEvent)
	if inputObject.KeyCode == Enum.KeyCode.R then--If the key was R then...
		print("Player pressed R")
	end
end
 function onKeyOff(inputObject, gameProcessedEvent)
	if inputObject.KeyCode == Enum.KeyCode.R then--If the key was R then...
		print("Player stopped pressing R")
	end
end
game:GetService("UserInputService").InputBegan:connect(onKeyPress)--This fires when a key has been pressed.
game:GetService("UserInputService").InputEnded:connect(onKeyOff)--This fires when a key has stopped being pressed.

As for finding how long a player has pressed R, or whatever key you want, you can simply put a loop in the function that fires when R has been pressed (onKeyPress), and in that loop you can count each second that has passed. When the key has stopped being pressed, the function that fires when R has stopped being pressed will make the loop stop.

Here's the visual:

function onKeyPress(inputObject, gameProcessedEvent)
	if inputObject.KeyCode == Enum.KeyCode.R then--If the key was R then...
		print("Player pressed R")
		Pressing = true--The function has just fired, so Pressing should be true
		Counter = 0--The time starts at zero
		if Pressing then--Start the loop(This won't stop until Pressing is false)
			wait(1)
			Counter = Counter + 1--After every second, the counter gains 1
		end
	end
end
 function onKeyOff(inputObject, gameProcessedEvent)
	if inputObject.KeyCode == Enum.KeyCode.R then--If the key was R then...
		print("Player stopped pressing R")
		Pressing = false--The Player has stopped pressing R, so stop the loop.
		print(Counter)--The amount of time the Player was pressing!
	end
end
game:GetService("UserInputService").InputBegan:connect(onKeyPress)--This fires when a key has been pressed.
game:GetService("UserInputService").InputEnded:connect(onKeyOff)--This fires when a key has stopped being pressed.

The Counter variable can only count every second. If you want to count in fractions of a second, then simply lower the wait(1) and Counter + 1 accordingly.