It depends on what you mean by Horizontal and vertical. These older Focal plane shutters tended to have blinds that had a horizontal slit that moved vertically for the exposure, like modern Seiko SLRshutters. Older SLR's tended to use cloth shutters with a vertical slit that moved horizontally.
Originally Posted by RalphLambrecht
When governed by tension and slit width like on a 5x4 Speed Graphic a horizontal edge of the shutter curtain slit takes just over 1/10th of a second to cross the film plane at the minimum tension #1, yet with the narrowest slit width this gives a shutter speed of 1/350th. So there's a time lag of 1/10th between the exposure at the top and at the botton, slightly longer if a wider slit is used.
Even at the top speed of 1/1000 which is at the maximum tension #6 there's a lag of 1/35th of a second.