I would say that "embarkation" is getting out of date, in our contemporary age. They may favour "boarding" over "embarkation". Perhaps use by navigation companies, though.
Of course, I don´t mean other related words, like "embark" etc.https://books.google.com/ngrams/graph?c ... ng%3B%2Cc0http://www.thefreedictionary.com/boarding
a. the act of embarking on an aircraft, train, ship, etc
Gramatically speaking, I think your sentence might be okay, but "when the embark is going to take place?/starts" would be a more natural version.