I worked full time while I attended college full time... while I raised three teenagers. It was tough. It almost killed me. I do not recommend it. But, part-time is a different story and, at 12 hours per semester, you are really taking the minimum (you need to complete about 15 hours per semester to finish in four years....)
This is what you have to think about:
The general guideline is 2-3 hours of study and homework for each credit hour you are taking, so...
If you sleep 8 hours per night and spend 3 hours per day showering, eating, traveling, etc., that leaves you, roughly, 13 hours per day (13 x 7 = 91 hours per week) for school, work, social activities, and rest.
If you are taking 12 hours, you will be in class approximately 12 hours per week:
91 - 12 = 79 hours remaining.
Studying for those classes and doing homework will require 24-36 hours per week. For purposes of this calculation, let's split the difference and say you will be studying 30 hours per week -- in addition to the time you spend in class:
79- 30 = 49 hours remaining.
Now calculate how many hours you think you will work... and any other activities that are a regular part of your life... family time, additional travel time, church activities, volunteer work, sports, music lessons, exercise, shopping, dating, movies, and so on.
Do you have enough time to do it all? If not, what are you willing/able to give up?
Remember, when you hear people say, "I don't have enough time!" that EVERYONE on earth has the same amount of time each day. YOU have to decide how to spend and prioritize that time.
If you don't have enough time to do something, it's because you have decided you want to, or need to, spend your time doing something else.