There isn't really a specific date on computer price cuts, it just happens gradually. Even current gen hardware slowly becomes cheaper. I know my i7 2600 started losing value shortly after it's release. Some parts will keep their price better than others, but eventually all computer prices will drop.
GPUs specifically fluctuate in price, CPUs prices generally tend to hold longer. In my personal experience, there is never a "bad" time to buy computer parts, as there will always be better prices and new hardware, but you can't keep waiting forever. I would get the best CPU available (because their functionality/value last longer) first, and get a second-generation GPU after that.