I recommend to be safe in contributing and do not get locked up when there are slots open. Contributing 5 images per day is good enough to receive alerts when there are more than 3 slot dates available. Aiming for top 14 ranks, to get the alert for any availability less than 3 is less useful because by the time you open the US Visa Portal, the appointment may already be gone.

Here is the email alert logic.. https://support.checkvisaslots.com/portal/en/kb/articles/what-is-the-logic-for-receiving-email-alerts