Improving a little on Hans Then's answer, we can just subclass the Timer function. The following becomes our entire "repeat timer" code, and it can be used as a drop-in replacement for threading.Timer with all the same arguments:

from threading import Timer

class RepeatTimer(Timer):
    def run(self):
        while not self.finished.wait(self.interval):
            self.function(*self.args, **self.kwargs)

Usage example:

def dummyfn(msg="foo"):
    print(msg)

timer = RepeatTimer(1, dummyfn)
timer.start()
time.sleep(5)
timer.cancel()

produces the following output:

foo
foo
foo
foo

and

timer = RepeatTimer(1, dummyfn, args=("bar",))
timer.start()
time.sleep(5)
timer.cancel()

produces

bar
bar
bar
bar

You can use the built-in time library:

import time


str_to_type = "The cat is catching a mouse."
start_time = time.perf_counter()

print("Type: '" + str_to_type + "'.")
typedstring = input()

if typedstring == str_to_type:
    end_time = time.perf_counter()     
    run_time = end_time - start_time
    print("You typed '" + str_to_type + "' in", str(run_time), "seconds.")

My humble take on the subject, a generalization of Alex Martelli's answer, with start() and stop() control:

from threading import Timer

class RepeatedTimer(object):
    def __init__(self, interval, function, *args, **kwargs):
        self._timer     = None
        self.interval   = interval
        self.function   = function
        self.args       = args
        self.kwargs     = kwargs
        self.is_running = False
        self.start()
    
    def _run(self):
        self.is_running = False
        self.start()
        self.function(*self.args, **self.kwargs)
    
    def start(self):
        if not self.is_running:
            self._timer = Timer(self.interval, self._run)
            self._timer.start()
            self.is_running = True
    
    def stop(self):
        self._timer.cancel()
        self.is_running = False

Usage:

from time import sleep

def hello(name):
    print "Hello %s!" % name

print "starting..."
rt = RepeatedTimer(1, hello, "World") # it auto-starts, no need of rt.start()
try:
    sleep(5) # your long-running job goes here...
finally:
    rt.stop() # better in a try/finally block to make sure the program ends!

Features:

• Standard library only, no external dependencies
• start() and stop() are safe to call multiple times even if the timer has already started/stopped
• function to be called can have positional and named arguments
• You can change interval anytime, it will be effective after next run. Same for args, kwargs and even function!

You can really simplify this whole program by using time.sleep:

import time
run = raw_input("Start? > ")
mins = 0
# Only run if the user types in "start"
if run == "start":
    # Loop until we reach 20 minutes running
    while mins != 20:
        print(">>>>>>>>>>>>>>>>>>>>> {}".format(mins))
        # Sleep for a minute
        time.sleep(60)
        # Increment the minute total
        mins += 1
    # Bring up the dialog box here