You can day trade futures or forex while having a full-time job. Simply, day trade before work or day trade after work. Basically, your day trading will impact your social life considering its occurring "outside" your normal work hours. Therefore, not advisable for the family person and not advisable for someone in a serious relationship. Thus, more suitable for the single person or for someone that has "odd" work hours.
In addition, you may be trading markets you don't like but that shouldn't be a problem considering your goal should be to be profitable and not married to some trading instrument.