I would say that "embarkation" is getting out of date, in our contemporary age. They may favor "boarding" over "embarkation". Perhaps use by navigation companies, though. Of course, I don´t mean other related words, like "embark" etc.Ref. thefreedictionary
A. The act of embarking on an aircraft, train, ship, etc
Grammatically speaking, I think your sentence might be okay, but "when the embark is going to take place?/starts" would be a more natural version.
When the embarking
is going to happen/to take place, etc.
Would be a more apt way to say that.
Let´s wait further comments on that one.