In response to the 5:35 pace for two hours in a runner with a LT pace of 5:30 you're right, of course that person couldn't do that but for a different reason. Looks at the central governor theory. It says that the central nervous system will only let the body recruit just enough muscle fibers for the amount of work necessary. This 5:30 LT pace person running at 5:35 is practically running at 5:30, hardly a big difference in pace. Now those two paces are so close that if a person physiologically can only run six miles at LT pace then how on earth is he supposed to run for twenty two miles at practically the same pace? His body knows that carb stores would be depleted and so his central nervous system keeps him running within his bodys metabolic limits.
You thinking aout LT pace as an exact to the second pace is very naive. LT pace varys all the time based on, alactic, glycolytic and aerobic energy systems fatigue. Also the level that the muscle fibers are filled with hydrogen, CO2 etc. The rate at which a runner becomes fatigued also has a lot to do with the pH levels of what are filling their muscles. Aerobic work producing less acid and anaerobic and alactic work producing more acidic waste.