Couldn't get edit to work, so will post again.
Re Navajo "lateness". It varies. Usually we would drive past the housing on the way to the little church and honk the van. Figured people needed time to clean up, dress, etc and then make it to the church. So mission staff might arrive up to an hour before church actually started.
As to how long to you wait? Well, if you have talked to so and so and know they are coming, until they get there. However long that takes.
BUT--that said--many in mission ministry on the rez were moving, at least when we left, to an "on time" basis for the broader sake of the Navajo. The cultural concept that time is truly expandable doesn't work well for them in school and on the job off the rez. So in accomadating that culture, you may be actually being kind of racists, assuming they cannot adapt to another culture in order to succeed.
It was a huge issue of contention, with some feeling it disrespectful to the Navajo not to wait and some feeling it was disrespectful to the Navajo to not hold to the broader cultural norm.
My feeling? Do the small outlying mission church the Navajo way, and don't expect every church in Farmington, Bloomfield, and Aztec to follow suit.
And surely don't expect some church in Peoria to run on "preacher time" or "late layman time" because that is what they do on the rez.