Perpetual timing

[Mark17]

As another use of a timer, I'm trying to do something like this:

import time

start = time.time()
y = input("What is 4 * 3?")
end = time.time()
while (end-start) < 4:
    if y=="12":
        end = time.time()
        print("it took", (end-start), "seconds")
    else: quit()

start = time.time()
z = input("What is 6 * 6?")

That is, wait until four seconds have elapsed before moving on if not input has been submitted.

Problem is the program stops and waits until input is submitted (when I did enter 12, I saw a running tab of elapsed time until four seconds... pretty cool!).

Is there a way to query continuously whether input has been submitted? If it hasn't then I would have it check time to see if four seconds have passed.