Yes every day or two. It depends on the number of twitter followers you have. It you close to 9000 like I do they won't all see your post. I've heard that a tweet has a life of about 15 seconds and while I think it may be a little longer think of a tweet like a commercial on television. Do it often enough to get noticed without being annoying.
Don't limit your tweets to things that just help you out or you may start to loose followers. Tweet about things that are of interest to your followers. If you are into cooking maybe mention that Good housekeeping has some new recipes. Don't always be self promoting.
A program that has a decent free automation system is Social Oomph. There is a paid version but for small tweeters there is more than enough functionality. You can post every hour if you lke from posts that you have pre-made. There is a link shortening tool built in to save on characters.