You hit a vague, never-quite-explained 5h window limit that has nothing to do with what you're doing, but with what every user is doing together. It's totally not downtime, you're just "using it too much" and they're telling you to fuck off until the overall usage slows down.

The order of priority is: everyone using the API (you don't want to calculate the price) → everyone on a $200/month plan → everyone on a $20/month plan → every free user.