For what it is worth I would assume in the alteration of this universe where Clark survived the bomding, they moved up the wedding date even more.
Actually, that leads me to what is probably the best reason to move up the wedding date. Well, two. For Lois and Clark here, the big issue is figuring out how two keep their two universes in balance, although with a time machine it might not be that hard, really. They could just retroactively export their children from one universe to the other.
From the perspective of establishing alt-Clark as local Clark in the minds of everyone around them, moving up the wedding date will seem the natural response to their friends after Clark was nearly killed in a bomd. Not that not moving it would look suspicious, but moving it looks more like the expected response. An unmoved wedding date would not draw suspicion, but a moved wedding date will lull people into thinking things are normal so that they miss any blips in Clark's stepping into the role of Clark.
