Back in the day and including Caribbean Island hoppers and Gulf air F27 flights in the 70s
LHR-Cyprus Addis Ababa Khartoum Seychelles.
HKG- Rangoon-Calcutta Rome LHR
BDA-JFK-MIA- San Juan -St Martin-Antigua
Montserrat-Antigua- St Lucia-Barbados -JFK-BDA
Doha-Bahrain -Amman -Istanbul AMS
Muscat-Dubai-Doha-Bahrein.
Longest distance in a 24 hours maybe plus a couple
EWR- DEN United DC8 -30, DEN- SFO United DC8-50 -SFO-LHR BA 747-200, as you might imagine that was not really planned, I was going home from Dallas but due to a family bereavement my colleague could not make the Denver meeting he but not I was due to go to had a sudden bereavement so I made good use of the time difference across the states leaving EWR at about 7 am getting to Denver around 0930, meeting and a quick lunch Denver to SFO arriving about 4pm for a flight about 6pm to London arriving early afternoon. I wouldnt fancy doing that at my age now. and security would have made it unlikely as well.