London city airport to Heathrow - is 3 hour s enough to make mid-day flight?

I’d say no. I think you’d need to reckon on 75 to 90 mins to get to LHR which would be very tight without delays. Also, do you need to clear customs and immigration at City?

Ooh wow. I can't see that happening:

• at LCY, you've got to land, get your bags, clear customs and immigration, and get to train. Min 30 mins?
• shortest train connection (DLR / connect to Eliz Line) is 1 hr 15 min (if you don't have to wait for train or connection at Stratford);
• check in and get to gate. Recommended 3 hr; min 1 hr?
• have to be at gate before flight. Recomm 45 mins; min 30 mins?

That's over 3 hours IF everything runs perfect.

I'd never buy a ticket that involved landing at one airport with the next flight at a different airport. Especially with only 3 hours in between.

If it was my trip I'd gladly pay extra a trip that doesn't involve having to cross London from one airport to another.

It is impossible if you have to be at Heathrow even just 2 hours prior to boarding an international flight.
It could take 3 hours just to get there from LCY.

Are you traveling on two separate tickets? If so, it just isn’t enough time.

Did BA sell you one ticket with this connecting time? BA’s website says 3.5 hours is the minimum connecting time between LCY and LHR (which I personally think is way too little). However, if you are on a single ticket you have some protections if you miss your flight. If this is one ticket from BA, I’d have a chat with them to see if you can change it.

Dear Rick Steves’ Community,
THANK YOU EVER SO MUCH!!!
Because of not only your reply, but also the promptness of your reply , I was able to successfully change my flight.
Time truly was critical. And get this: there was actually a flight from Florence leaving a little later than my original flight, arriving directly at Heathrow with a two hour layover, then arriving into New Orleans at the original time.
To answer the ticket question: it was one ticket - sold as Florence to New Orleans with a connecting flight in London requiring change of airport. I foolishly assumed that the time would be sufficient!

good result! yay