Every social network has different posting rules. The general sweet spot for posting frequency on Facebook and Twitter is 2-3 times per day, however you can tweet more often because the lifespan of posts tends to be very short.
Try not to make more than 7 new posts per week on Instagram. Posting twice in a day is not forbidden, but one post a day seems to be the network norm.
Post between 4-10 times per day on Pinterest.
There’s no drop-off in engagement for posting more.