Why should the block move at constant speed in procedure 2.?

If the angle of the board is such that the component of gravitation force equals the force of (kinetic) friction, then the net force on the mass equals zero. Any slight nudge to set it in motion (static friction is always bigger than kinetic friction) therefore will result in a motion where no net forces act. According to newtons first law, uniform motion (constant speed in this case) results.