I presume that you know you are over the $675K estate tax deduction, so you should be thinking about some estate planning, and perhaps those pros will help with this problem too.Timing and dollar cost averaging have a lot to do with where you expect the stock market to go. If you think it is high and likely to crash, then stretching out the purchases over 5 yrs is safer. If you think it is likely to keep going up, then the sooner you buy the better. If you are like most of us, unsure, then buying in a series of purchases over some time frame makes sense. But you have to choose the time frame.Personally I wouldn't do a single index fund purchase that large. I would at least spit it in half and do them at least a month apart. But your portfolio is reasonably well diversified, so it may not matter in your case--especially if you are a long term investor.