I would request a refund on the basis that a roughly 10-hour change is a cancellation, whether F9 changes the flight number or not. If you are denied a refund initiate a chargeback with your credit card issuer (bank) making clear that F9 cancelled your flight and then rescheduled it for 10 hours earlier. Have a copy of your e-ticket receipt and your cancellation (change) notice and upload or otherwise provide them with you chargeback.

Not worth arguing at a time when F9 (and other carriers) are trying to preserve cash.

If you want, you may also file a DOT Complaint on the same grounds, e.g., 10-hour change is a cancellation and DOT rules require a refund for a cancellation.

Having nothing to do with Covid-19, the fact that F9's own COC do not provide for a refund at a reasonable point, e.g. 90-120 minutes is a good reason not to book F9 in the future.