At what point in the Strike Witches timeline does Brave Witches take place?
Yes, you are correct.  To be specific, BW's episode 1 takes place around SW's episode 6, considering the time lag of news traveling at that period.  The creator Fumikane gave that tidbit of information through his tweet (Japanese)


  で、1話。新聞に載っている坂本と宮藤。扶桑に情報が来るラグを考えると、ストライク1期の6話あたり、隊全員が一つのチームとして機能し始めたころ撮られたものでしょう。