Hi Ambalal Raibagi,
I am Dave, I will help you with this.
There is currently no setting or even a registry hack to set the default to 25 minutes, that will default to 30 minutes and must be manually set to 25 minutes each time.
The best option is to open the feedback hub (Windows Key + F) and provide your feedback on the lack of functionality and suggest that Windows stores your preferred time in Focus Mode in Windows 11 to the developers there.