Accidentally pressing the wrong button on the timesheet can be very annoying. While working on the next revision to our timesheets we have been trying to find better ways to prevent mistakes. We have tried different button orders as well as different positions, and found that while it improves the situation for some people others find it harder.
The solution which we found that worked the best was to get rid of the need to save entirely. By automatically saving changes as they are made users do not need to press save at all, eliminating the chance of pressing the wrong button.
We are getting ready to launch our latest timesheet revision, so this should be available soon (depending on the functionality you use).