It’s actually 18.49 hours, or 18 hours and 29 minutes.
Use your well being hours! They will expire at the end of the year. Those are the only hours that will not roll over into the new (calendar) year.
Edit: If you’ve been working more than your average hours each week lately you can still use your well being hours. Go back through previous weeks and add as much as you can until your 4 hours are used up. I believe you can go back to the beginning of September. We must’ve had a MyTime update around then because I couldn’t bulk up any weeks in August or earlier.