If you've accidentally clicked 'start job' before it was time, you can reset the button in no time.
On the web portal, go to the job details page of the job that needs to be updated.
Click the arrow icon above the 'start job' button.
A window will appear for you to confirm. To reset start job, click 'unstart job' in the bottom right.
'Start job' will now be cleared for you to click again at the correct time.