Hello Greeshma,
If you completely stop the workflow, save it, and then restart it does the issue persist? If a workflow was running, then was paused, altered, and resumed, the previous underlying workflow job doesn't get changed and will still execute with the previous configuration. Performing a full restart clears the underlying job and refreshes it with the new execution criteria.
Just from what I'm seeing here, it's the only scenario that I can think of that would cause your workflow to kick off prior to the scheduled time.
Regards,
Craig