Ok Good Question. 1st to hide the clock go to cydia en install the lockscreen clock hide then go to setting and you will have a menu there enable it. for the Slider move the lockscreen theme the in winterboard to the top so its on top of all you themes. that will do the work.
i was checking mi iPhone n i have a slider theme active i think this is what missing install this theme and activated it is call "clean lockscreen 4.0" but keep the typoPhone theme on top of all the others. hope this will fix it