Interesting Iron Man challenge!
U can still increase the difficulty playing on HoF (U should drop your 60 days limit though)!
If at least one character survive vs goblins in Targos haven (nice challenge without pausing&reloads, especially in the warehouse), I'll sincerely congratulate U!
Actually, it's a good training when U know that any goblin could inflict U 60-100hp damage at a critical hit in melee. If U switch later to the normal mod, U'll be not surprised at all at 72hp by Queen Worm!
If U wanna speed challenge then skip all unneccessary battles using Invisibility/Hide. I tried this challenge in IWD1 on HoF and finished just in few ingame days.
Tc, Yigor