It is hard to give you an exact answer, because it will depend at the speed the company hiring you produces the required documentation, and if they have been already approved to hire foreigners or not.  From a weel or two, to maybe even a month.

Once you have all documents in hand, The Embassy has two types of services, one is standard, and takes about 3 to 5 days, depends on Embassy location,  There is another service called "expedite", cost a few dollars extra, but if you submit application before 10 am, you can pick the visa later in the afternoon.  I always use that service to avoid paying extra nights in hotels.

Two weeks for your FEC when the school receives your documents, this is depending on if you do your medical in Hong Kong, they will mail this back to you and it takes about 3 to 5 days at the Chinese embassy in Hong Kong if they still have the one day service out of service, once you enter China it's a trip to the PSB with your foreign administrator, takes about two hours then 5 days until the R visa is given