I did a return run KUL to JHB a few months back. Something like a 7am outbound and 8:30am return. No problems. Walked off the plane at JHB. Stood at the gate, walked back on. Security is very chill on these domestic flights. OLCI no issues. It was on two separate PNRs as i couldn't book the return with such a short turnaround. Also to note it was HBO.
Same crew. No questions asked. Just a smile and a hello again cx_newbie.
For my BA tier runs, I like to add a 2,000+ sector to mix things up for the 140TP level. Usually decent fares to India (Delhi / Mumbai both qualify). Incheon also had a very good sale recently too.
You should also consider PEN. It's the only domestic airport with a lounge.