I'd use a NIST Time Source and have my SharePoint syncing with the NIST Time Source.
Your approach would break when you went mobile or the time was off on the SharePoint server. Why design for failure?
Note: This is my first encounter with the SharePoint 2010.
How to create a clock synchronized with the server time on my SharePoint Portal? I would also like to create buttons for start-time and end-time and record the duration between two on a daily basis for my organization i.e. daily an employee will click on start time before starting their work and click end-time before leaving. We need to record this duration. How do I have achieve this and using which software/technology/programming language compatible with SharePoint 2010.

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