DNSSEC - Zone Signing and Key Signing Keys

Have you read this link?

https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/bigip-dns-services-implementations-13-0-0/6.html

I don't play with DNSSEC very often, but let me try answer the questions:

What is the function of the rollover period in relation to the expiration period?

Rollover period is when both keys are valid.

What is the best practice value for the rollover period?

The manual talks about 21 days.

What happens once the Expiration Period ends? Will I need to recreate the keys?

You should had already created a second key before that, during the rollover period, so that key should be valid.