Back when I was still writing fanfiction I wrote episodically. Meaning, I was aware that I'd be posting in instalments, or chapters, so I planned my story breaks accordingly.
I have always felt that once I committed to posting that I owed it to the gentle readers to post at least once a week. For me a chapter, or instalment was generally between 10 and 14 pages long.
I got in the habit of writing until I hit 10 pages then looked for a logical stopping point. Sometimes things got carried away, and the chapters ran long, but most of the time I was able to reach that goal.
What I've been trying to say in my round about way is that I feel 10 pages of a once a week post is an acceptable minimum.
Tank (who doesn't really like significantly shorter posts because not much can be developed story-wise in too short instalments)