You were too slow command

Question

I have this number guesser code, and everything works, but I would like to make a command that will print 'you were too slow' if you take more than 20 seconds.

This is the code:

import random
def guessr():
    choice = int(input("Guess the number the Game(TM)\nType 1 to play\nType 2 to have the computer play."))
    if choice == 1:
        guess = int(input("Your guess? "))
        Rnumber = random.randint(0,100)
        while guess != Rnumber:
            if guess < Rnumber:
                print("Your number is too low.")
            elif guess > Rnumber:
                print("Your number is too high.")
            guess = int(input("Your guess? "))
        print("Good job! The number was",Rnumber,":)")
    elif choice == 2:
        Rnumber = random.randint(0,100)
        guess = 0
        while guess != Rnumber:
            print('It is not',guess)
            guess = random.randint(0,100)
        print('The number is',Rnumber)
guessr()