You mean to pick their brain? If so , linked in search, send request and short message (ie don't pick brain in opener) then call them on the phone next day and ask them q's. Booking time to chat via linked in prob good idea too given their interviews Scheds. Ps if looking for mass feedback tell them you'll send survey link after your call. Recruiters like the face to face, to be heard etc. should work out well for you