I’d put it all in the market now.
I look at it this way: you have two years’ of savings in cash now and are wondering what to do. Pop it in over the next 4-8 weeks and continue to invest the additional savings according to the same allocation you’ve chosen. If you have kids, I’d bias heavily towards equities as with your stated figures, you’re saving for their lifetime, not yours, (Yours is already a lock, basically, assuming you can save $500K post-tax for each of the next 5 years.) If you don’t have kids (or don’t want to give them meaningful money), I still say stay fairly equity-weighted, but then figure out what you want the rest of the money to be used for. You’re likely to have many years of relative surplus (over the $100K projected spending). I wouldn’t keep such a large cash position. Consider trimming that to $200K or so and creating a bond or CD ladder that you use for your “fortress of solitude” SHtF money. With $5MM in the market, you’re likely to cash over $75K/yr in dividend checks anyway, so you really need very little supplemental to avoid having to sell in a down market.
You’re well on pace to win the game in crushing fashion. First, shore up the next five years of high savings (including managing taxes over that span). Then, plot of out how little cash cushion you’re comfortable with and trim towards that outcome. For you, making sure you get that $2.5MM invested is more important than whether you put the existing $1MM in now or over the next 3 years.