From the look of things, the void universe can't even control the white sphere perfectly. It can only use part of its power, which means that it needs to slowly accumulate power before it can activate the Time Lock.
This gives him a short window of opportunity to stop what the void universe plans.
So Legion-1 thought to himself, "I have to stop it before it can activate the Time Lock. If I don't, then there might never be Legion in history."
There is a lot at stake here. The existence of Legion as a whole is at stake. So he used all of his power as he shot towards the void universe.
He and the other clones are aware of the iron grip that the void universe has over the flow of time in the void universe and the time loop that makes people forget what they have done.
