When are Neil Patrick Harris and partner David Burtka having twins? "Whenever they choose to come out," Harris joked to TV Guide Network's Chris Harrison. "I think it's up to them really. I'm guessing fall."

Neil Patrick Harris and partner expecting twins

Harrison, also the father of two, gives one great piece of advice to the How I Met Your Mother star: Sleep now!  "Oh, is that how it works? I thought it was the other way around," jokes Harris. "I thought since they go to bed at 7, you can just hang out and sleep all night."

Check out the video below, where Harris also gushes about Glee co-star Matthew Morrison: