The 737-400, at heavy landing weights at Johannesburg (sorry ORT IA), obviously temp related, suffers from a 53min turnaround restriction. This defintitely hinders turnaround times and can be a real issue in the summer months. The 737-300 is not limited as well as the DC9/MD80. I'm not sure about the -800 as in present SAA config it is not an issue but with the extra seats etc there may be a problem.....or maybe Boeing has resolved the issues of the -400. Would be interesting to know!
As far as IRS alignment is concerned....you know that you either have time for a long align or a short align....the choice is yours and does not play a role in any form of turnaround restrictions whatsoever......!!!