Like you, I have a full-time job and have to find time to study.
If you have something near the top of your lessons page that looks like this.
and next to the exam that looks like this.
This is a new feature Penn Foster has added to help give a more realistic school feeling. that one would get to complete assignments and exams if sitting in a classroom and had to be ready to take the exam on the exam date. These are not hard dates, but recommendations. The Set your exam schedule has 3 options, by default it is on "Recommended". The date next to the exam you can click on the change. However, you do not have to use Penn Foster's new feature. Each semester allows for 1 year to complete everything. I suggest if it stressing you out, and it sounds like it is, either switch it to the "Extended Plan" (which spreads out the dates more), modify the dates to a more comfortable time frame (the dates are click-able and changeable), or create your own study schedule. The dates are only suggestions and there is no penalty if you miss the date listed. The only date you need to worry about missing is the date is the "Program Expiration Date", which will you find at your "My Courses" page under the "Program Summary".
Hopefully this helps as I can hear the stress.