I concur with todao about watching the dough instead of the clock. Generally I find that smaller batches take longer to proof, not less Maybe an artifact of my process...
Just when I think I have it perfected I'll go for a two or three week stretch of sucky bread. My crappy bread is still better than what they sell in the grocery store here though.
Cardinal rule in bread making - Never Watch The Clock; Always Watch the Dough.
To respond more directly, No, you don't need to adjust the fermentation time relative to the size of the loaf. Remember you've already scaled down the ingredients (Water/flour/salt/yeast) and it's their relative percentage within the formula that determines how the dough will respond. You adjust the fermentation period based on how the dough is developing. When it's approximately doubled in mass (I generally use an 80 - 90 percent increase in mass to avoid over proofing) it's ready for the next phase.