How long is the training for a proper Japanese tea ceremony?

The answer depends on many, many variables. Which specific ceremony, where it will take place and for what occasion, who will be attending and various other questions. In general, to learn the most basic way of preparing and serving tea will take most students 6 months to a year, but to put on a full-length (4.5 hour) ceremony will take at least 5 years of minimum once-per-week study.