Do you really believe that Chapter 1 Limitations, 1.7 Engine, 1.7.2 EGT limits is saying the material used for the turbine blades is happy for continuous use at 849 degs C?
From a metallurgical point of view, it's TOTAL TIME AT TEMPERATURE that counts. Whether that's 5 minutes today, 5 minutes tomorrow, 5 minutes next Monday - or whether it's a half-hour all at once - makes little difference to the molecules!
(In fact, I'd argue that one cycle of 30 minutes is less fatique than 6 cycles of 5 minutes.)
The 5 (or 10) minute regulatory limit is plainly outdated in light of modern materials and technology. Instead, it serves a convenient CYA function for manufacturers.