How much time to allow from Harwich disembarking to Heathrow flight?

[Phishface]

THe cruise I'm considering disembarks at Harwich supposedly starting at 4 AM. I would need to disembark, then take the 2-3 hour train whenever it comes to Heathrow. This assumes:
1. the ship arrives/disembarks at the time they promise
2. I really could theoretically disembark as early as 4 am
3. trains really do run to Heathrow starting that or very early.

What do you think is the earliest time of day that day I should safely book a transatlantic flight back to the US?

[ollienbertsmum]

Would you really get off at 4 am?? You book a private car to get you directly to Heathrow, but I looked at nothing earlier than 2 pm. I think "Why go on vacation and then leave yourself at risk of a drama at the end.?"

Early in the morning trains can be cancelled, there can be traffic jams, extra security. Just my opinion

[Globaliser]

Originally Posted by Phishface

THe cruise I'm considering disembarks at Harwich supposedly starting at 4 AM.
...
What do you think is the earliest time of day that day I should safely book a transatlantic flight back to the US?

The first weekday train to from Harwich International to London Liverpool Street at the moment looks like it's at 0710, arriving at 0848. (There are earlier departures at 0542 and 0627 but both require you to change trains at Manningtree.)

You should allow an hour to connect from Liverpool Street to London Paddington for a Heathrow Express train, and then another 30-40 minutes to get to check-in from the time the train departs from Paddington. That would get you to check-in at about 1030, so your earliest safe flights are going to be from about 1300 onwards if this is how you want to do it.

If you got the very first train of the day at 0542, you'd arrive at Liverpool Street at 0710, so basically 1½ hours earlier. But even with a scheduled 0400 arrival, you'd have no guarantee that you'd make an 0542 train.