We did it last summer. You are assuming that everything goes to plan! In our case, on landing at T3 they sent us to a bus gate. Then they couldn't get the stairs in the right position to disembark the aircraft. 20 minute delay. Bus trip to terminal. Long walk to transfer station and bus to T5 just left. Had to wait for next bus. Hair raising ride and then enter T5 to escalator where we are disgorged into the mobbed general security line. Left us with 20 minutes in the lounge to grab some food and get to the departure gate, which involved getting the train to T5C and then enter the general scrum for boarding. And all that took 3 hours and left us feeling that we had run a marathon!