U.K. and Ireland - One more LHR transit question

Mods, please move if necessary. Arriving on UA from ORD at T1 connecting to TG at T3. The Heathrow Airport Guide is a bit confusing. It states that it's just minuted via a pedestrian tunnel but then also that it will take 60 minutes by transfer. What's the correct information? I have 3 hours to play with. Thanks all.

If you have 3 hours then you have no problem either way.

If your luggage is checked through or you have hand luggage, then you can transfer airside. The walkway you have read about is landside.

The airside transfer involves moving in a bus. The landside involves clearing immigration and going out (passport and visa issues possibly?), a VERY long walk down the walkway and then clearing back in through security. Quite frankly the hassle is not worth it, I would stay airside.

The airside transfer time could be about 15-30 minutes, but the landside could easily be over an hour as you have to go through the immigration queues at the border leaving T1, and then the security queues to get back into T3. The walkway alone will take you 15 mins if you are healthy!!

Thanks. Luggage is checked through. Will look for the bus then. Happy holidays.