There is no straight forward answer to your question. The answer is "it depends." There are many factors you need to consider. For example, what is your age, are you single/married, what is your immigration status, what is your socioeconomic status, why do you want to do PhD, what major you want to get in, how many hours you currently work, what exactly you do at your work, what are you hoping that PhD will bring in your future life, etc.