Hi
Looking through various memoirs gives various answers. Common is the statement that a Flight took off five minutes after another, indicating that probably an individual Flight had taken off together. Other times it is mentioned that they took off ‘with’ another Flight or even elements of another Squadron from the same aerodrome. it could all depend on the operation I suspect, eg. if one Flight was to fly high cover for a lower flying Flight then it would make sense for the former Flight to take off first so they could climb to height. I believe that most Offensive Patrols by the RFC/RAF were generally of one Flight so taking off roughly together would also make sense as it would ‘speed up’ getting into their ‘patrol’ formation without wasting too much fuel.
But that is just my ‘take’ on the question.
Mike