Everyone keeps mentioning about the Sunday April 27 date as "the" date.
However, in many cities that have multiple congregations in the same KH, there are meetings on Saturdays also.
In our KH (and many others locally) there are 5 congregations in the KH. Three congregations have their meetings on Sunday and two on Saturday,
So unless the instructions are such that the letter can't be read before April 27, it should very well be public on Saturday (actually Friday if you take into consideration countries in earlier time zones).
Rub a Dub