That's a very personal decision which doesn't work the same way for everybody. BUT, if it was me... I would continue the part-time job for as long as I could. As you move into the nursing program, it will demand more time from you for clinical hours and lastly your practicum.
Working full time and nursing school is not impossible, but it is grueling! If science comes easy to you, you should do just fine. BUT, thre is always that employer that might give you a hard time when you ask for a flexible schedule to accommodate your clinical hours. Some see it as an advantage to them (depending where you work), some as "why should I give you flexibility when you're just going to leave me"?
Do you have a support system in case you loose your job half way through the program if you needed the help? Think and plan for this possibility.
Are you married? Have kids? If so, forsee how you would tackle challenges along the way (finances, child care, lack/reduced quality time with loved ones).
Hope this helps.