Wow, I go all turbo mode-ish, here.
A while ago I beat FF2 in five or so days, and now I suddenly beat FF1 in TWO days!
I didn't even tarry very long at Elfland, during the Ogre massacre leveling moment, which took about two hours (*hint* Power Peninsula *hint*).

I started this crazy thing during the evening, the day before yesterday, and then I managed all the way to Melmond in four hours.
The next day (yesterday), I played some more during the afternoon, and made it to the Water Shrine.
Then, during the evening, I beat the Water Shrine and the Mirage Tower, and then I went straight to the final dungeon and just breezed through it!

Wow, I never made it this fast before, it probably took about 10 hours!