To collect 24 hours' worth of data using a packet capture on a Cisco Secure Firewall Threat Defense (FTD) appliance without prematurely stopping due to buffer size limitations, the engineer should increase the packet capture buffer size. The default buffer size is 32 MB, which is insufficient for extended captures.
Steps:
* Access the packet capture configuration on the FTD device.
* Increase the buffer size to 1 GB, which provides a significantly larger capacity for capturing packets over a 24-hour period.
Setting the buffer size to 1 GB should accommodate a substantial amount of traffic and prevent the capture from stopping prematurely.
References: Cisco Secure Firewall Threat Defense Configuration Guide, Chapter on Packet Capture Configuration and Management.

Reference: https://www.cisco.com/c/en/us/td/docs/security/firepower/601/configuration/guide/fpmc-config- guide-v601/fpmc-config-guide-v60_chapter_01100011.html#ID-2101-0000000e