I would give yourself like 2-3 dedicated evenings to be sure, even with well put together CV, longer otherwise.
It's not something to procrastinate too much on.
Also, it will depend on how many programs you apply to as well, that takes some time to add in.
You don't want to be scrambling on this.
Start the demographic section and past ed section right away. Even if you don't have the full list put in any programs you already know you want, or at least start that list separately.
Things that depend on your school's or other organizations' speed should be done the moment you can, like getting token, sending photo for upload, sending for transcripts, authorizing USMLE score upload.
I say give yourself more rather than less time so you have time to proofread, proofread, proofread. You may find yourself scrabbling/googling for little details more than you thought, like DOI # for pubs, contact info for EC's you've done (what was their email again? Phone number? Let me sift my email to find month I started that) figuring out average hrs per week on stuff you might have done years before, and then proofreading more. You get to put descriptions on stuff you've done, so you want to be able to write, rest, read, write, rest and repeat until you've painted yourself in the best light.
It gets very tiring and a rush job is not great. I had a well put together CV and still found it exhausting and put a lot into it, and still forgot to put a great EC on there (not that that ended mattering, just peeved to have left it off).
Get going. Every bit you do now gets you closer to done on time.