If you're worried about a harsh correction, then perform Dollar Cost Averaging over a period of time(6-12 months) depending on the amount(6 months for anything less then 20k we'll say).
Could it crash right after that period? Sure.
Does anyone know anything? No. The talking heads are as worthless as fucking horoscope writers. With such titles as DOW 36000 just prior to the .com bust, and whatever the hell they were writing during the financial breakdown.
Corrections happen. You know what you don't do during them? Sell.
Buy. Buy buy. Buy. Buy buy buy. Buy.
Things go down? Keep buying.
Everyone's happy in a bull market, if you have money in it, you're making money, hurray! Profits come when you buy at low prices... which is when everyone is very, very unhappy. If there's blood in the street, it's time to buy -more-.