Sked supports caption lengths up to:
Instagram: 2,200 characters
Facebook: 2,200 characters
Twitter: 280 characters
LinkedIn: 700 characters
On Instagram, posts with longer captions can sometimes be harder to post – if you are posting long posts
On other social networks, you can enter captions up to that length. Keep in mind if you are scheduling for multiple accounts at once, the maximum caption length will be the length of the 'shortest' platform (e.g. if you are scheduling to e.g. Instagram and Twitter, 280 characters).