The necessary change has to be made in osd_api.c, but this file is not open-sourced at the moment. Updating it on GitHub will take some time, so this workaround is provided to help you continue your work for now.
If you do not wish to display AM/PM, kindly use osd_time_fmt_12
If I use latest Github code with the shared libispfeature.a by you, will it create any other problems due to version or API mismatch? because the libs has different file size.