In the SEPMAC.cnf.xml:
In your config file, try changing the dateTemplate to M/D/YA
This website is extremely handy for customizing your configuration files but also addresses how to set things up if you load SIP firmware on the phones:
https://usecallmanager.nz/sepmac-cnf-xml.html
But also understand this: UseCallManager Patch and Cisco Phones