Hi Bob,
Actually, on the RT system, the "wait until next multiple" and the "wait" RT functions have µs accuracy. When we started the development, we tested using a timed loop versus timing with a "wait until next multiple". The timed loop had a timing accuracy better than 1/1,000,000 while the "wait until next multiple" had a timing accuracy of only 1/10,000. However, in our application, we are happy with anything better than 1/100 timing accuracy. There are a few drawbacks in using a timed loop. The most important one is a 10% cost in CPU speed. We could not reach our goal to run a demonstration at 1kHz with the timed loop while we could with the "wait until next multiple".
The RTETT seems like a good idea but I suspect that not that many people use it, probably because it is so hard to understand... and it is hard to understand because not so many people use it.