Planoly won't work for you since they do not offer LinkedIn scheduling. Also, you can only schedule posts on Instagram and Pinterest which may further be shared over Twitter or Facebook.

Can you post directly from Planoly?

Planoly allows you to share your Instagram posts directly to your connected Instagram or Facebook page when scheduling auto-posts. You can utilize this feature to post your photo's caption, content and location tags.

Is Planoly only for Instagram?

Planoly is devoted to just Instagram. While I personally haven't used Later for anything other than Instagram, the option is there. This feature doesn't seem to limit Later's depth of features for Instagram since the tool was originally built as a dedicated Instagram planning software.