when was this supposed to be set?

I loved this movie but the I'm confused by the costumes. The setting is czarist Russia, in St. Petersberg. But after the revolution, from 1914, there was no czar and St. Petersberg was called Petrograd, and later, of course, Leningrad.
Yet the women seem to be wearing "modern" (as of 1927) clothes and hats. The men's military garb doesn't tell us much (except that those high-high collars must have been a pain).
So what's with the costuming? I don't get it.
Thanks for any explanations to come...