Depends on how good you are at that time of game and how much patience you have. 
+1
I beat it in the 90s without a walkthrough, took me about a month. I was more into arcade-style games than dungeon crawlers/RPGs back then, so I'd typically play for an hour or so at a time before getting bored.
Nowadays, I have a lot more patience and focus. YMMV.
