Fisherman,
I've heard similar explanations of Numbers 33:3 on other forums, but they do not (IMO) come to grips with the language of the verse.
Some translations, like YLT and KJV explicitly use the words "morning" or "morrow" and others, like the NWT emphasis the back-to-back linearity with phrases like, "Directly the day after the Passover" and "The very day after the Passover"
You've suggested that the word "day" should be understood as a reference to the calandar date, as opposed to the normal, unglossed meaning of the word, yôm, but your reason seems to be more of a desire to harmonize JW teaching when what is needed here is a valid textual basis.