When I decided to just do it and get Longinus Zeta, all I did was farm Sastasha (normal). While it was in the bonus window, I only had to do it once per mahatma. When it wasn't, I was would farm Sastasha two, three times tops, to max out a mahatma. It was about 5-5 1/2 minutes (unless I had to afk, then it took a couple of minutes longer). Though I never thought about doing Ifrit (normal). I should do it just to see what it's like to solo it.