How early?
 

I will be flying out of Heathrow to Entebbe at 7:25 PM. How early should I arrive at Heathrow? (It'll be following a layover and I'd like to do a bit of sight seeing during the delay)

On the way back I'll be flying out of Heathrow to LAX at 11:55 AM. How early should I arrive then?

Thanks!

A lot depends on the airline you are travelling with. Generally, arriving 2 hours before is fine, even more so if you use the check-in machines most airlines have.

If you are on Virgin, American or United, you will be using Terminal 3, which generally has longer security line-ups than Terminals 1 and 4 (used by British Airways). Even then, 20 minutes usually gets you through the line. As you're off to Entebbe I assume you'll be on BA for that flight at least.

The evening (for Entebbe) will generally be quieter than the day, so you may be able to cut the time down to 90 minutes (but personally I would still aim at 2 hours or just under that).

If your connection is same day, you may be able to get a seat assignment and boarding pass before you leave the airport for the city. In that case, you could arrive just over an hour before (especially for the Entebbe flight) and be fine.

Welcome to FT, emeybee!

Can you tell us more about your complete itinerary? What time do you arrive into Heathrow before the long layover? Where from? Which airline(s) are you flying? In what class(es)? Do you have one ticket for the entire journey, or two?

Similarly, on the way back, when do you get back from EBB to London? Are you staying in London overnight before you fly to LAX?