Ok, we'll talk about an idea of the moreфон. It's about writing >= 5 sentences everyday.
Btw, why 5, why "sentences"? What about 50 words or 250 letters or 300 chars? What is a reason for choose this "magic size"?
Next, the author expected that users would correct errors of each others. I don't known a situation in Instagram, but it seems that almost nobody do it in Italki.
And here is interesting question: are all fixes correct? I think this is a pretty good example of Impostor Syndrome.
As a result, it turns out that nobody check your posts or smb who do it may have level of language less than your. So, what is a real reason for public journaling in this case? Inspiration? Come on. Prizes? Come on - 2.
Conclusion: if you want to journaling, just do it; you may use any conditions, any format, any incentive, without waiting moreфон, it isn't so perfect.