Need Script based condition to restrict time sheet booking for given planned for attribute
One answer
No. And JavaScript based attribute customization is also not going to work with a probability of 0.99999999999999999.
Comments
The only chance I see would be using an advisor/precondition on work item save.
The Timesheet APi is explained here: https://rsjazz.wordpress.com/2015/03/31/the-work-item-time-tracking-api/
Timesheets is information linked to work items using a special link. So there is a good chance that you will be able to detect changes to them in work item save and a precodition/advisor could detect if it is allowed to save and prevent it from happening.