Blackbird nest in porch

A few weeks ago I noticed a pair of blackbirds building a nest in our front porch (it's open fronted) on top of a stack of logs. Since then I have seen the female blackbird sat in there a couple of times, but nothing for at least a week now. Is it likely they are still going to use the nest or is there a chance it has been abandoned? At the moment I've cordoned off the porch so they wouldn't get disturbed but if it is likely it's been abandoned then we can reinstate our post box again! Could anyone suggest whether we are best continuing to leave it alone?