Investing multiple millions in Emaxis – all at once or spaced out?

I already have a chunk invested in emaxis (S&P and All Country) for retirement, but I have also accumulated a decent sum (20M+) that I intend to add to it.

So far, I've been dollar-cost averaging by investing it at 1M a month for the last three months. But I'm starting to wonder if I should just chuck it all in at once and forget about it.

The markets being at highs and yen being at lows, it doesn't exactly seem an ideal time to do this though. Note that I will still make (smaller) contributions from my salary even after it's all invested.

Appreciate any thoughts.