Looking back at my own records, I popped the $700K barrier in March of 2012, which would be in rough range of your $718K figure. By February of 2015, I had broken the $1M barrier. However, I didn't stay permanently (so far at least) above the $1M barrier, until April of 2016.
It's hard to really pinpoint a precise number on how much you need to invest, because there's just too many variables. How the market does, what you're invested in, and so on.
In my case, I can't tell you how much additional money I put in for that March 2012-Feb 2015 period, but the data I do have is:
2012 (whole year): $28,723
2013: -$17,811. For some reason, I cashed out more than I added that year. Can't remember why, but I might have been trying to pay down on an HELOC.
2014: $35,570.
So, if I was to take a wild guess, I'd say I put in an additional $45-50K during that timeframe.
Of course, as the old saying goes, "YMMV", "Past Performance is No Guarantee of Future Results", "Yadda-yadda-yadda."