Four minutes is plenty of time to walk up a few flights of stairs or taken the elevator. The facts and evidence place LHO in the SN at 12:30.
There were some guys on the 5th floor at the time. Anyone could have been walking up or down the stairs or using the lift at that moment. Do you really think your calculated LN Oswald would walk up the stairs or take the lift (with minutes to go), when he could have been seen by any lingering employee?
You then have him zooming back down to the Domino room after the shooting? Ludicrous.