So, 'tenpo la' means, literally, "at a/some time", not "occasionally" ("at a few times") which is probably better for "sometimes", except literally. 'tenpo la' is also standard for "Once upon a time" at the beginning of fairy tales. 'ken' has nothing to do with time.
Well, since I don't push any point unless I see that it is pretty regularly used and that others criticize its misuse, I stick with my claim to be descriptive and reactive.
"Official" does have a meaning and, since there is no certifying agency (aside, perhaps, from community consensus, but even that isn't certified). there is no official anything, just common usage, highly respected usage, roundly condemned usage and so on. Sorry, that is just the way the language is set up -- like English but not French, say.
pu is indeed prestigious, but that does make it official (cf the Queen's English, note that even Sonja does claim that i is official, though she does say her book is, which is hubris). The common dialect of most users (if there really is one) is no more official than pu's; it is just what most people use. That is an advantage for writing on these sites. Of course, so is using pu, since everyone recognizes it. And Pije's and even Lope's and 76 Lessons'. None of them are really official because, as noted frequently, nothing is, just like in English. (tp has the advantage that no one has even put out a style book yet.)