If a 3L will create enough yeast for your pitch then just do the one step. You’ll be done in half the time.
I prefer brewersfriend for yeast calcs because it’s a little more conservative and easier to calculate stepped starters from what I remember about mr malty.
There is always room for discussion. I prefer the Brew United pitch rate/yeast starter calculator for what seems to be a more realistic estimation of yeast viability.