I've posted on there before before I got a new account, and the one that had the most engagement was updated on random afternoons since I was still trying to find a good schedule. I think Friday around 3~5 pm would have worked best, but that was earlier this year.
Now I'm posting on random afternoons again to try to catch a good time XD. I think from 3-5 still works, but I don't know which days are best...