Question about time scale of getting an editor
How long does it take on average between sending a query to agents and getting a contract with an editor?
Also, how many agents is it advisable to send a query too at one time.
That's really difficult to say. The first step is getting a contract with an agent. For some people, it happens quickly. For others it can take many months (if it happens at all).
You have to consider that agents get thousands of queries each year. A good agent will spend most of their time working on behalf of their existing clients, so reading queries or slush (submissions) is something they do in their spare time only.
There are some factors you can influence to your advantage - such as targeting agents interested in your genre, following submission guidelines, and writing a good query letter. But luck also plays a big role. So does the quality of your writing (especially after you have send in a manuscript).
Once you have a contract with an agent, the amount of time it takes for the agent to sell your book to a publisher depends on the agent's skills and the relationships they have in the industry. There are no guarantees.
Keep in mind that authors such as Stephen King, J.K. Rowling, and J.R.R. Tolkein had their first books rejected numerous times before being sold. That's where luck and perseverance come in. The process can literally take years in some cases. Weeks in others. It is certain that some fantastic books don't get published because the authors give up after a few dozen rejections. It's also certain that many bad books get submitted dozens of times because their authors believe in them. For every bad book that gets published there is probably a good book that gets sent to the writer's attic.
I don't know if I am inspiring or disheartening you, but that's the crazy nature of this business. There is no definitive answer to your question. You have to decide how much you believe in your book - based on objective evidence from other people as well as your own assessment. Then see if you have the stamina to take dozens of rejections and still be willing to keep querying and submitting.
You have to decide when to quit, and you have to make sure you don't quit too soon.
Of course, there's always a slim chance you'll be one of the lucky one's who sells to the first agent you query. But don't count on it.