Python - obtener tiempo al fnalizar hilo, no en su ejecucion

import thread

import time

import timeit

t1 = time.time()

t2 = time.time()

t3 = time.time()

t4 = time.time()

listadeimp = []

def imp1(b1,t1):

	for x in range(0,b1):

		b1=x*x+7*x+10

		listadeimp.append(b1)

	print(time.time() - t1,"seg")

def imp2(c1,t2):

	for x in range(b1,c1):

		c1=x*x+7*x+10

		listadeimp.append(c1)

	print(time.time() - t2,"seg")

def imp3(d1,t3):

	for x in range(c1,d1):

		d1=x*x+7*x+10

		listadeimp.append(d1)

	print(time.time() - t3,"seg")

def imp4(e1,t4):

	for x in range(d1,e1):

		e1=x*x+7*x+10

		listadeimp.append(e1)

	print(time.time() - t4,"seg")

def main():

	global b1,c1,d1,e1,t1,t2,t3,t4

	b1=26

	c1=51

	d1=76

	e1=101

	thread.start_new_thread(imp1,(b1,t1))

	thread.start_new_thread(imp2,(c1,t2))

	thread.start_new_thread(imp3,(d1,t3))

	thread.start_new_thread(imp4,(e1,t4))

	print(listadeimp)

main()