Ok.
You understood the equation I provided?
You can already do it.
All you need to do is divide the desired total word count by your intended session target.
It’ll tell you how many writing sessions are required to reach your goal.
The problem, as far as Scrivener is concerned, imho, is that you are asking that be integrated a basic calculator to it, which would display a “days left” count, based solely on a calendar, and that has nothing to do with your actual word count per session.
You could design a tiny excel sheet and link to it, you’d get just that.
Question:
In your vision of things, what happens / how should Scrivener behave if you miss a day?
Or/then, if you set your session target to 500 words, and one day happen to “only” write 499 ?
If it is only a matter of pre-establishing a reachable deadline based on your personal writing habits / performances, @kewms already gave you the best answer you’ll ever get.
See what you can objectively achieve for an average, and use that variable in the equation I provided.
[Target manuscript word count / your comfortable average = sessions required.]
Or take your days off into account, and rather use your average per week. Same equation, it’ll tell you how many weeks you need for your deadline to be comfy.
. . . . . . . . .
To be honest, if I were you, here’s what I would consider optimal. (Because your request is legit. But simply lacking, imo, the tracking factor.)
Establish what is your comfortable writing average per session. (Go by @kewms’ advice.)
Divide the desired manuscript word count by that. You’ll get a number representing how many writing sessions it’ll take.
Count that in a calendar, taking into account how many days a week you write. That’s your deadline.
Set that deadline in Scrivener, along with writing days per week. (If you write four days a week, just select four days, any (it doesn’t matter which, from monday to thursday – it’s not like Scrivener would prevent you from writing on a day off…), and check the “allow writing on deadline” option.
Scrivener’s calculation should give you, on day 1, exactly what was initially your personal average.
From that point on, your session target will fluctuate according to each of your sessions’ word count.
You’ll get an accurate report on your progress and what is to be done, on a writing day basis, to reach your goal in time.
As I said earlier : If you write less than your session’s target, you’ll later have some catching up to do. (The session target will increase.)
If you write more than your goal, you can relax. (The session target will go down.)