I want to clean the cache once per day. For me, the whole point of paying for Cache Cleaner Pro was to not have to learn how to do cron jobs, which are different depending on which hosting plan one is using. Therefore, the response referring me to the cron jobs page in your documentation is not at all helpful. Also, in Cache Clean Pro, the maximum interval for automatic cache cleaning is 25200 seconds, which is 7 hours, so...also not helpful. I really feel like I wasted 29 Euros.
Spend 10 minutes investigating how cron jobs work and how to set them up, and you have what you want.
Out of curiosity, if you bought Cache Cleaner for that specific use case, why are you only now seeing you cannot do this with the interval setting 5 weeks after buying?
You can increase the interval to 24 hours.
But that still won't let you clean it at midnight. It will clean it the next time you log into the admin (unless you set it to frontend) and the last clean is at least 24 hours ago.