On iPhone, you can add both your image and your caption straight from the Boards Keyboard into Facebook's scheduler or any scheduling tool.
- Open Facebook (or your scheduling tool) and start a new post.
- Tap the Image you want to post.
- Tap the text field and switch to your Boards Keyboard.
- Tap your Text script to add your caption. Tap ABC to make any edits.
- Choose your date and time, then schedule the post.
Using Android?
Download the image from Boards first. Then open the Facebook app, upload the image, and schedule your post there. See Saving Images and Videos to Your Phone.