I don't know myself, but I found this:
They will give you the evolutionary stones after you defeat them in a rematch.
School Kid Alan at Route 36 - Wednesdays - Firestone
Fisherman Tully at Route 42 - Sunday Afternoon - Waterstone
Lass Dana at Route 38 - Thursday Night - Thunderstone
Picnicker Gina at Route 34 - Sunday Afternoon - Leafstone
Twins Kay & Tia at Route 15 - Saturday Night - Oval stone
Not sure if it's true though.
I'm pretty sure the one in bold is crap, because I just called her about half an hour ago and she just had the usual message for me.
I might've just phoned her too late, but I thought "day" lasted until 8pm...
