I've done a lot of work with hosts on various shows. One guy stood out more than others on being so natural on the vamp/stretch to fill the time. Starting at 5mins, we give one minute signals. Not once did it ever sound unnatural in trying to rush or filled with ums, uhs, or ahs. Others struggled with the rushing being most noticeable.
Jonathan Agnew has a similar story about the late, great Australian cricket commentator Richie Benaud, although filling ~52 seconds rather than 5 minutes.
I think it's every host's worst nightmare when they see it when reading the teleprompter. It's my worst nightmare when watching local news feeds where they are clearly off prompter or vamping.
