Any time after take off if you check the VLS on approach page it is calculated from estimated landing weight which is equal to ZFW+EFOB at destination. It remains constant as long as EFOB remains same.The actual aircraft gross weight is not taken in consideration, but if you activate approach now the VLS immediately changes to VLS for present aircraft weight. It is not frozen at that weight but will vary with the aircraft weight but is not noticeable as it changes only1KT/Ton.