The "rolling 24-hour window" means that WhatsApp looks at the number of templates sent in the previous 24 hours to determine whether the messaging limit has been exceeded; there is no  'reset time' for the WABA.

To ensure the limit won't be exceeded, we suggest counting the template you've sent in 24 hours prior to the request.

For example, if you would like to send messages at 1 pm, the amount that can be sent in this time period is the messaging limit (i.e. 1000) minus the number of messages sent in the 24 hours before 1 pm.