Plan A: Change your environment; spend three hours a day preparing a proposal for management/ownership to work as a contractor paid by entry opposed to an employee paid by the hour. Find the relevant tax and overhead savings to make this a mutually beneficial arrangement. Find out who in management/ownership can approve your proposal and who it just creates headaches for, buy beer for both.

I understand that goes against the spirit of your question, that your work environment may be to rigid, management that could approve the proposal are out of reach of the data entry staff, or one of many other arguments, but 60 hours a month is a large amount of time, it is shocking what could be done.

Plan B: Now on to things I've actually done in that situation; spend 60 hours preparing a bulletproof argument/presentation for a raise, spend 60 hours learning how to create better resumes, spend 60 hours learning how to job hunt without a resume (handshakes and recommendations), spend 60 hours job hunting, and last on the list spend the time on entertainment so that you are mentally recharged to make the most of your personal time.

I can't concentrate if the words I'm hearing are not the ones I'm typing. Ebooks would be a terrible distraction for me during data entry. Music without lyrics would be better.

During blank minutes at a call center I used to work at, I made slow progress at writing a novel. It was made more enjoyable by the quirk that my writing flows better with pen and paper.

Post to lesswrong.com.

Tried something like that. Was unable to do anything productive after 5 hours without a real deadline.

I would start programming mobile games, and would hope to make money from them. If I don't succeed, at least I had a hobby, and maybe can use the experience to get a more interesting job later. If I do succeed, then I do not have to solve the problem of boring job anymore.

That would require sufficient freedom to spend those 3 hours not just programming, but also painting pictures, editing 3D models, editing levels, and testing the game on the phone. Okay, hypothetically that is not necessary; there can be some parts that I have to do at home. But it would be much more convenient if I could do whatever is necessary for the game immediately when I need it.

Or, if I wouldn't have a specific plan, I would just learn random stuff from online universities. I enjoy learning, so I wouldn't necessarily care about how useful are those lessons. I would imagine that some part of that would be useful somehow later, if nothing else, then for impressing people.

Someone who is a buddhist could use those three hours to meditate daily, and achieve nirvana in a few years, while keeping a well-paying job. Also, being a buddhist could help with the feelings of boredom from the job. ;)

Renegotiate work time to 5 hours.