There is no cut and dry answer to this question because editors all work differently. Some concentrate on one project at a time. Others, juggle a couple simultaneously. Some work only weekends and evenings, others only work 9 – 5, Monday through Friday. Still others only work ten hours a week. Some editors take four weeks to complete what others may complete in four days. It doesn’t mean one editor is better than the other, either. Freelance editors are independent business owners who set their own schedules. If you need someone to rush through 100k manuscript while holding your hand every step of the way and is available for random phone calls on a Tuesday afternoon—you probably should think twice about working the editor who is only available ten hours a week after her day job.
Deadlines and other expectations are why you should always, ALWAYS work with a contract—whether your own or the editors. The start date and completion date should always be in that contract. Sometimes, different milestones in between need to be listed there too [e.g., layers of editing (see Q1 above), response times to questions or edits (editor AND author), conference call days/times, etc.]. Think about what you need or want ahead of time. Rush jobs cost more. Don’t wait until your query gets you a manuscript request to ask an editor to edit your novel overnight. Don’t tell your editor “whenever is fine.” Work out a date. Put it in writing.