I have a sign up in my office: Perseverance + Perspective = Success. Basically, I believe that if you’re not willing to work hard, you probably won’t (and don’t deserve to) find true success; and if you have your priorities out-of-whack, you won’t find it either. So for me, time-management boils down to evaluating what matters most and then working hard and sacrificing what I need to in order to accomplish that.
That said, it’s impossible for me to tell you how much time you should spend writing each day since I don’t know the other obligations and responsibilities you have. I will say, however, that if you have an already full life, and you’re planning on adding writing to the mix, something will need to give.
Personally, I don’t write every day. I write most days and, honestly, I’d say I don’t take enough days off from it, but I’m not the kind of person who would tell you that you need to write for an hour a day, or write a thousand words a day, or something arbitrary like that—especially if I don’t know what your life situation is right now. Look at your professional duties and your spiritual, relational, and physical health goals, then evaluate what you can eliminate or re-prioritize to pursue your writing.
As far as how to spend your writing time (the type of project you should work on) there are a number of factors to evaluate. A novel might take you 1000 to 1500 hours to write. Think about that—if you put in an hour a day you’re looking at three years or more of writing.
Also, with the publishing industry in flux, it seems that novellas and short stories are having a bit of a comeback (at least in e-book publishing). So I would say, only attempt a novel if you have a story that requires that many words to tell. If you can get by with writing it as a short story, go that route. Save yourself and your readers time.
If there’s any way you can do anything else other than writing, do it. If the stories are burning in your soul and you start to go crazy because you have to get them out, then do what you have to in order to give them birth. It’ll be a gift to yourself and to the world.