and from my experience, you always fight at least two battles on the way out, so it would probably be around 5 min, i don't think i've ever gotten there in under 3
normally, but i do like to take my time... even when life is on the line

.
depending on the strength of the enemies, and how difficult it is to flee/kill them quickly, the times could be 5, 10, and 15, or just 5, 8 and 10

. the prize could be extra money for the middle, a potion for the highest time (to be evil

), and either a piece of materia, such as quake, which you do not get for a while normally, or even just bigger money boost/higher item like an elixir.
also, i am not entirely sure how much can be put onto the psx image, you'd likely have to rearrange everything on the disk if there wasn't enough free space in the file you were editing, or something compressed too big (kernel and scene issues), so you may be pretty limited in that category

.