Oh, boy. Lemme see..
If you write once a day, you’ll be faster altogether, no matter your actual, down-to-the-keyboard writing speed. More time spent over copy simply amounts to a faster wrap up of said copy. During the best NaNo days, I was prone to writing several times per day, too, but I’m quite aware that that’s highly unsustainable if writing’s not your primary job, if you have small children and/or if you want to keep your sanity. (Yust saying. YMMV.)
If you write (at least) a few times per week, you’ll probably have an easier time keeping everything in your short term memory (if that’s where you need it – it’s definitely where I prefer to keep it), you’ll have an easier time getting the copy finished and – almost as important – you’ll minimaze the actual whining time you have to spare. As of early 2020, I have a hunch this might be my sweet spot, but there’s still that issue I have with winter, so I’m not getting my hopes up. (Personally, I’m currently either in the ‘every day’ or the ‘a few times per year’ category, no middle ground yet, dammit.)
If you write a few times per month, you’ll probably manage to keep everything under control, stop your plotline threads from getting too loose, and keep a general grasp over where your copy is going. You’ll have time enough to do your research (unless you’re of the organized type and you manage to cram everyhing in your everyday tempo, which, well, not just anybody can do, yeah?), you just might afford bigger time slots for your romantic dates with your novel, and you’ll be more than able to track your progress, because, you know, continuity. Try not to get too sidetracked with other novel ideas, and you’ll probably do just fine.
If you write a few times per year, say, in bouts of a few days at a time or so, and keep it up for a few years, you’ll still be writing in continuity, although I honestly cannot see how anyone would keep the concentration necessary for keeping the story in check, nor resume said concentration every time they go back to their novel. (I certainly can’t – and it’s taken me literal years to finally understand that it’s not even worth trying.) Still, if that’s your jam, by all means, go for it!
To rewing a bit; If there’s one thing I can’t stand, it’s other people putting their own habits out there as guidelines for people they’ve never met, whose everyday lives they cannot begin to comprehend, and who would, most often, be much better off listening to their own gut, than some distant online advice person. Still, isn’t that exactly what I’m doing – or trying to do – here? In a way. But you’ll never catch me
reading mainstream literary fiction saying, I dunno, you should write XY number of hours per day, or at a certain time during the day and/or week, or plot novels this way, or construct characters that way. What I will say, over and over again, is find out what works for you, do that and, no matter what, don’t give up.
And, calendrical equations aside, the true answer to the initial question is actually quite simple – if you want to do it, if you enjoy it at least half as much as a lot of us do, you probably ‘should’ write as often as you possibly can.
…but you didn’t really need me to tell you that, now did you?