There's a different deadline for supplementary estimates (C) than there is for main estimates. As you know, it depends on when the last allocated day is. We still don't know the deadline for supplementary estimates (C), but we do know it's much longer for the main estimates. Because all of the days have not yet been allocated, the firm date for the deadline at this point is unknown.
On March 2nd, 2022. See this statement in context.