Book dropbox visa slot soon after visa extension is filed

[dacca]

Is it possible to do so? Traditionally I'd wait until I have 797 in hand but Dropbox slots in my country seem to be getting taken at rocket speed. So I am wondering if it is any beneficial to go ahead and book the slot (and update the document number later). My company has filed for an extension in premium and I need to travel in end of November. Home country is India.