There's a lot of uniformed guff being written about BA ops here. What you are missing is that the BA commercial and ops departments write the schedules, not the crew. If the BA aircraft has a 5hr schedule break in SSH it's because the powers that be have decided thats when they have slots, or when they have aircraft free, or when the customer profile dictates it wants to fly. Charter companies can flog their aircraft round the clock because there are tour operators who'll fill the things regardless of the flight timings. Start planning flights on a scheduled airline at weird times and you find that customers drift to competitors who offer more convenient timings.
Another nonsensical comparison quoted on here is the KLM A340 AMS-CAI flight (since when did KLM operate A340s?). BA could operate LHR-CAI-LHR in a day with a single crew, but it would either leave so early it would miss all the inbound connecting passengers, or return so late it would miss all the connecting outbound flights. What do you think would cost BA more: nightstopping a crew or making the service non-viable for North America connections?