Blog post frequency

Ideally, you should blog once a day. The more quality content you can produce the better, but be consistent in the timing of when you publish your posts. If you can create three blog posts a week, post them evenly throughout the week. If you can create 14 blog posts  during the weekends, post them twice a day, throughout the week.
I haven't found 'specific' information regarding how website update frequency effects SEO, but I have notice increased traffic/Google rank when I post daily and consistently. It shouldn't come as a surprise that Google may pay attention to something as seemingly arbitrary as post frequency. Google already considers websites more trustworthy for being listed on DMOZ, and Yahoo Listing only because most sites that are listed there tend to be of higher quality.

Control when your posts are published using WordPress

WordPress is ideal for controlling when readers and search engines see your posts. You can publish your blog posts as 'Drafts' and then schedule when they will become public using WordPress's publish scheduling feature. The publish scheduling features can be found at the top right of the 'Add New Post' page. By default, your blog posts are made public as soon as you click the 'Publish' button, but the actual publish date can be modified by clicking on the 'Edit' link next to 'Publish immediately' in the 'Publish' area.