The page https://www.theoi.com/Nymphe/NymphaiPleiades.html states:
"The Pleiades were seven mountain-nymph daughters of the Titan Atlas. Their leader was Maia the mother of Hermes by Zeus."
I can't actually find anything in the translations on theoi.com to support this. In fact, there does not appear to be any story in which the Pleiads actually work together to achieve any sort of common goal, and so it doesn't seem to me that they would have had any sort of leader at all!
A possible exception might be the missing story from the Epic Cycle in which the Pleiades are members of Artemis's hunting party (see my earlier question: Artemis and the Pleiades). But even then, surely Artemis would have been the leader, not one of her attendants!
Robert Graves, in his Greek Myths, makes an equally-unsourced claim that Alcyone was their leader. As well as failing to cite any sources, Graves offers no supporting detail as to what the Pleiades might have been doing that needed a leader.
Does anyone know what the original source was for the Maia-as-leader claim? Or, at least, for any of the claims that they had a leader at all? If so, do you know what it was that she actually led them in doing?
Edits based on comments:
The star Maia is roughly in the middle of the Pleiades star cluster, so couldn't be either the first to rise or the last to set.
Maia was the oldest of the Pleiades, and I have wondered whether "leader" just resulted from a mistranslation of "oldest".