Considering how fast ghasts will notice you before you try to kill them... ain't nobody got time fo' dat, ain't nobody got time, ain't nobody got time, ain't nobody got time fo' dat!
I guess it will be a bit longer, because the fire charges will put out lots of fire, therefore making it easier to walk into fire... again, even within a 4x4 area. (P.S., how do you know that I generally go prepared?)
Be prepared. Ghasts' fireballs are not that fast, and considering you are saying they hover over lava, far away.
I facepalmed at this. Going into the nether without armor is suicidal.