I finished my Bachelor's degree while working full time with the previous tuition program Disney had. I have now started my Master's with the Aspire program. The work/school balance really depends on where you are working and the school schedule you decide to take. When I worked in the parks, my work hours were all over the place and I found it difficult to get into a routine and come up with a study schedule, but I have a lot of friends who are currently doing this -- and are successful. I've since transferred over into an office gig and I am finding it much easier.
The balance is really up to you, though. I took a lot of time off before finishing my degree, so I wanted to graduate as soon as possible and took a full-time course load while also working full-time. It was a lot. You have the option to take only one or two classes at a time though -- whatever is most comfortable with you.