As with the above, any price rises won't go down well around Christmas.
However, there is never a good time to announce price rises! Customers are not going to say, “Thank the lord this price rise was this time of the year”!
Concentrate less on the timing (although best wait until the New Year) and more on the announcement. Explain in detail and try and turn the price rise announcement e-mail into a positive. For example; if you’ve had no price rises for a long period (say 3 years) make a point of it; if the price rise is due to the rise of a commodity (like material costs) explain it in detail.