When it comes to manuscript writing, many authors wonder how long would it take for them to complete. Well, the timeline for manuscript writing for journal publication varies depending on research complexity, author experience and journal requirements. Furthermore, writing the initial manuscript writing for Journal Publication draft may take a few weeks to several months specially if the extensive data analysis is involved.
Additionally, revising and refining the manuscript to meet journal standards often requires additional time. After the submission, the peer review process can take anywhere from a few weekes to several months. 
Also, the reviewers may request revisions which can further extend the timeline for the completion of the project. You also need to make the multiple rounds of revisions to make sure everything is perfect before the final acceptance. In short, manuscript writing is considered as a long-term academic process rather than a task. By proper planning and time management you can avoid the delays.