Ever since HMG has updated the immigration hall at T4 I have found the operation to be SUPER quick and incredibly efficient. I remember waiting 1.5 hours or longer at LHR and LGW.

Now at T4 I've never waited longer than 10 minutes to get through immigration. T4 is the SkyTeam terminal (except for a few remaining pmCO flights that still use it). At worst you'll have a couple of DL flights arrive around the same time. But the hall has 30+ immigration stands available for EU and non-EU arrivals. They usually have at least 8-10 running on the non-EU side for the US bank of arrivals in the morning.

Bottom line...should be quick. But like the NY lotto, the motto "Hey you never know" definitely applies.

-RM