time allocation for social media post

I have decided that I want to give 2 hours to create 1 social media post.

Sometimes I can write content within 15 mins and sometimes no matter how much I stare or try to think, I can’t come up with content to write.
Or even if I know what I want to write, it doesn’t sound right or I don’t like what I have written. Sometimes I can’t express what I have in my mind onto paper.

Then I get frustrated and just avoid working.

And this feels like out of my control because my brain just doesn’t come up with ideas or my brain isn’t efficient at that moment. And then I get mad on top of it because I want to share content but now am not able to do it.

Is there a way to come up with ideas and present it well when my brain has just frozen.

Second question: What do I do with 1 hour and 45 min that I have scheduled for that day during times when I am able to finish it in 15 -30 mins?
I realize those times get really unproductive or I do busy work because I haven’t scheduled anything else at that time.