Period for service of questions—tribunal cases5
In proceedings before a tribunal, a question shall only be admissible as evidence in pursuance of section 74(2)(a) of the Act—
a
where it was served before a complaint had been presented to a tribunal, if it was so served within the period of three months beginning when the act complained of was done;
b
where it was served when a complaint had been presented to a tribunal, either if it was so served within the period of twenty-one days beginning with the day on which the complaint was presented or if it was so served later with leave given, and within a period specified, by a direction of a tribunal.