It seems that the market always is going down through the first 3 weeks of October, which ends on the third Friday which is "triple witching" options expiration's. (Note the Jack-O-Lantern).
The big crash of 1987 was on Oct. 19th if you will note. So right after "triple witching" is probably a good time to jump in if you are a market timer. Many years have December rallies and also January is the beginning of a new year and people are full of optimism and new year's resolutions, including the stock analyst at the major firms. They need to prognosticate the big "new winners" for the coming year.
Also on the monthly front is the famous "Sell in May and go away". The thinking is that everyone on Wall street is taking their vacations and spending all that money they made during the beginning of the year. They do not want to leave open positions while they are on the beach and not paying attention to the market. So probably not a bad month to lower some of your stock positions and raise some cash.