It's always a struggle trying to find a steady rhythm when you need to be self-motivated about something - heck it's hard enough finding any sort of rhythm at all. Right now I'm tackling not only a loose schedule of one ~5000 word erotic short a week, but also the weekly modules of my degree and monthly essays looming on the horizon. I feel like things would be a heck of a lot simpler if I was doing just one or the other, because right now I often feel like I'm compromising the first area of work if I spend too much time focusing on the second. Hopefully down the line I'll have more freedom to defer modules of my studies or take a month off writing when I need to knuckle down, but for the time being I can't really afford to neglect either in these early stages.
So how do you find that sweet spot of productivity on such a vague and loose schedule? I'm not a fan of setting strict guidelines and work hours for myself (even though that works out great for some people) as it tends to circumvent the whole benefit of being self-employed in the first place. Right now broader deadlines seem to be working pretty well for me. "I'll get one story done within this one week period", "I'll take two weeks here to work on this essay", "I'll need at least three days to get this chapter read".
As long as there's plenty of planning ahead, plenty of wiggle room, and plenty of time to get everything done, my sporadic schedule seems to go just fine for me.
Plus, if all else fails I know for sure I can fall back on "Just sit down and do it".
And I mean, that simplest solution is really the best one when it comes to any form of creative media. Time and again I've come across people who've been very talented in one area or another, but never get their dream off the ground because they tend to treat it as a hobby rather than work.
Spoiler alert: no job, no matter how fun, ever stops being "work". Creative pursuits can be incredibly rewarding and enjoyable, but there's still some element of an uphill battle there every time you sit down to focus on them.
So I just sit down and do it. Just do it. Just write, even when you're not feeling into it. I'm going to make this my goal in order to hit my self-imposed deadlines in the future, and I know for a fact that plenty of uninspired beginnings have turned into productive several-thousand word sessions once I get in the mood!
I don't think there's ever a point where most writers feel completely and utterly comfortable with their own productivity, but there's definitely a point where you start to become more and more comfortable with meeting the demands you set for yourself!