So using HC-110 times isn't what I would advise... But maybe 3 minutes longer than HC-110(B) times. Which is probably 9 minutes for a 100 speed film.
Well, I did say to start there. I was going to add that more dilute would probably give less grain and goodness knows, 110 needs that! He will have to work out the times that suit in water temps he will work with in Singapore.