Imo if the 3rd party memory of relatives of Stanton is accurate, that Oswald was seen by
Stanton around the 2nd floor lunchroom staircase just BEFORE Stanton left to go outside to the front steps of TSBD., then it was probably approx 12:12 at the latest. Stanton got outside and was on the steps probably right AT 12:15 having preceded Mrs Reid and Carolyn Arnold arriving slightly later.
I don’t see any conflict with Carolyn Arnold’s 12:15 2nd floor lunchroom sighting of Oswald or a latter possible 12:25 front lobby sighting, because it all fits with the theory Oswald having gone outside in watch the P.Parade just as FBI agent Hosty notes recorded.