Hi Tarna - a little over an hour.  About 10 minutes to assemble equipment and ingredients, peel and slice potatoes and onions, 20 minutes for for 1st cooking of potatoes, another 25 to 35 to cook after eggs are added, a few minutes for suspenseful showtime (flipping the tortilla, getting it back into pan), a few more to brown other side.  It should set about five minutes before serving.  It does require attention and concentration - from slicing the potatoes carefully and evenly, to gently nudging edges of tortilla away from pan as it's cooking - something I enjoy as my mind is always skittering, and it's almost meditative. 

 

I'd actually tried it once prior to Spain - a friend from Venezuela brought it to a party as appetizer. It was fantastic and disappeared fast, but she complained it wasn't her best effort.  Funny how good cooks will disparage their dishes, fussing that the spices weren't quite right, the one they made last Christmas was much better. :-)