So long as you have some margin on VLS, 50' is fine, the thrust reduction is smooth and as you flare you touch down on speed without any float. If the speed is right on VLS then wait 'til 30'. Either way, if it hasn't touched within a couple of seconds, relax the flare and put it down, also the 330 needs to be flown onto the nosewheel, it is a long way up in the air at touchdown. As the spoilers and reversers deploy, there is a nose up tendency which needs to be guarded against.