What a wonderful photo, especially the back
The lady at the extreme left of the front row, and maybe a couple of others, are wearing an outfit called a suffragette suit, a fashion that came out in October 1910 and lasting until 1915.
As the ladies are mostly wearing hats it's not easy to see their hairstyles, but the hat styles with the prominent brims don't really look like 1920s fashion to me.
Hem lengths also look a bit low for post-war.
There are an awful lot of men in the photo and none in uniform, so unlikely during the war years. I'm going to guess just before the war, 1914-1915 or so.
Cheers,
China
