Instagram does not allow you to schedule Collab post from Instagram.com or from Meta Business Suite.
Here is how to schedule a Collab post for the future:
Using OneUp (the social media scheduling tool) you can schedule a Collaborator (Collab) post on Instagram for the future.
OneUp allows you to add up to 3 collaborators at a time on your Collab post.
When your post is ready and you’ve added your collaborators, you can schedule the post and choose what date and time it will post.
OneUp is one of the only social media scheduling tools that supports scheduling Collab posts on Instagram. It also has a ton of other features. Check it out here: www.oneupapp.io