The plan you're subscribed to will determine how many posts you're able to schedule in advance.
|Plan||Scheduled posts per social channel|
This is not a daily, weekly, or monthly limit, this is the number of posts you can store in each social channel's queue at any one time.
For example, if you're on the Free plan and you already have 10 posts in one of your queues, you wouldn't be able to add any more until the queue count for that channel is less than 10. Put another way, if you share 1 post per day, you'd be able to schedule up to 10 days in advance on the Free plan.
It's good to keep in mind that we also have daily posting limits in place for each social network, which you can learn about here.