you must know the total travel time

after that you must configure the parameters of frames per second (ftps)  and the path animation parameters as frame and  Evaluation time.

that is a simple rule of three


![configuración path][1]

also you can calc the length of a Bezier curve please check: [http://blenderartists.org/forum/showthread.php?206790-Length-of-a-Bezier-curve-in-2-5][2]
or you can try with my script that will print the lenght in console:

    import bpy, bmesh
    
    for area in bpy.context.screen.areas:
        if area.type == 'VIEW_3D':    
        
            ob1 = bpy.context.active_object # this is the curve
    
            bpy.ops.object.duplicate_move(OBJECT_OT_duplicate={"linked":False, "mode":'TRANSLATION'}, TRANSFORM_OT_translate={"value":(0, 0, 0), "constraint_axis":(False, False, False), "constraint_orientation":'GLOBAL', "mirror":False, "proportional":'DISABLED', "proportional_edit_falloff":'SMOOTH', "proportional_size":1, "snap":False, "snap_target":'CLOSEST', "snap_point":(0, 0, 0), "snap_align":False, "snap_normal":(0, 0, 0), "gpencil_strokes":False, "texture_space":False, "remove_on_cancel":False, "release_confirm":False})
    
            bpy.ops.object.transform_apply(location=False, rotation=False, scale=True)
    
            bpy.ops.object.convert(target='MESH')
    
            bpy.ops.object.editmode_toggle()
    
            obj = bpy.context.object
            me = obj.data
            bm = bmesh.from_edit_mesh(me)
    
            edges= [e for e in bm.edges]
    
            total = 0
            for edge in edges:
                
                total = (total + edge.calc_length())
    
            print("total: ",total)
    
    
            bmesh.update_edit_mesh(me, True)  
            bpy.ops.object.editmode_toggle()
            bpy.ops.object.delete(use_global=False)
    
            ob1.select = True
            bpy.context.scene.objects.active = ob1


  [1]: https://i.sstatic.net/edEB0.png
  [2]: http://blenderartists.org/forum/showthread.php?206790-Length-of-a-Bezier-curve-in-2-5