Originally Posted by
lespoir
Generally you do not need to clear immigration because you do not intend to enter UK. But connecting flights still require another layer of security check, so sometimes it can be quite a slow process. If your AC flight is not delayed, then 2.5 hrs is usually considered to be OK. Less than 2 hours from gate to gate would depend on many things.
Based on past experience for a T3 to T3 connection, as long as you have at least an hour and no bags to pick-up the connection should be makeable.
2.5 hours is more than enough.