Although March 26 is the last opposition day of the cycle, it all needs to be reported back three days before. That's how supplementary estimates are designed. To deal with motions of supply, the last supply day is March 26. Mark it back three days and it's March 23. All supplementary (B)s have to be back to the House or deemed reported back as studied, even though we might not get a chance to study them.
On February 24th, 2020. See this statement in context.