I don't think a call for sites is a requirement of the regs - to be honest, the regs on plan preparation have very little in them these days so in theory there is scope for a great deal of flexibility at this stage. However, I would regard a call for sites as good practice and an essential element of getting started, at least for site allocations DPDs, as it helps you as an officer find potential sites in your local authority area and is a first round of consultation, particularly for developers/landowners who are obviously very keen to put their sites forward. In practice, while call for sites tend to be time limited (6 weeks) I have accepted submissions outside of the formal consultation period, so long as a site is considered alongside all other potential sites in the draft plan. You might want to check SA regs as well to make sure there aren't other aspects to consider.
