but not at the expense of writing great content on your site that drives people to want to read more and sign up for your newsletter.
... or that will attract others to link to your site without you requesting.
It's an interesting question, and I don't have a right answer. I think most miss the concept that it is not purely a function of time. I can spend zero time on a site when it comes to link building, when the quality attracts links on it's own. Based on the comments from previous posters, if in that situation I would reduce my link building time and shift some of that focus to building the quality level of my site so it attracts links from others.
Link Building = Time + Quality