Hi there. It's under a 5 minute walk from hotel to Hatton Cross underground and, after waiting on a train, less than 10 minutes to T5 where I normally fly from. I think Terminal 3 is only one stop as opposed to the two for T5 (It's been a while since I last got off at that stop) so I'd say around 15 minutes - 3 to walk to Hatton Cross, 3 to wait on the train, 5 for travel and 4 to walk up to the terminal. Hope that helps.