Every day around the same time my hive does their orientation flights. Is this a sign of a continual growing colony or are they just stretching their legs and getting some flying time in? 
. Does anyone know if these are always newly graduating bees?
Amazing to watch, but I have to explain to friends because it can be frightening to see for the first time.
Totally normal bee behavior. Mine do it most between noon and 3pm. Bees do not poop inside the hive (unless they are sick), so when they gotta go, they gotta fly! When a bee emerges, she starts life as a nurse bee. Nurse bees are generally photophobic (avoid direct sunlight), however, they will leave the hive to orientate and poop. Then by the time time they become foragers, at around 21 days old, they know the local hive area and can find their way back home after longer flights.
Don’t park your car under their orientation zone though, unless you like sticky dark yellow spots all over it! 
Or leave your washing out 