135 training really depends on the company. I've arrived at a company with current 135 elsewhere, been given a fast crash course on company indoc, a quick flight, and sent for a checkride with the POI. I've arrived with another employer, very 135 current, and been given two weeks of indoc, nearly three weeks of factory training, thrown in a pool, put our fires, given training between points, days of approaches in the soup, and then a FAA checkride, resulting in weeks of training, and the longest took a couple of months or so. In other cases, I've been tossed the books, told to go home and study, be ready for a checkride the next day. Then another, then another, until I was checked out in all the aircraft.
Generally it's basic indoc with company material, then whatever's needed for the type of operation and training. If you're going to FSI or Simuflite, then you've got that time to consider.
Compared to 121 operations, where I've gone over two months with the initial training and type, then nearly six months total getting online before going right back for recurrent...the 135 has always gone fairly quickly.
Your own experience will vary with the operator, aircraft, type of operation, etc. Be wary of those who push you too quickly or give inadequate training and preparation. Don't agree to a checkride until you're ready; it's your reputation and certificate on the line.