Longer Cycles
Whilst I am unaware of the intricacies of your Duet's cycle programming, I am aware on my Miele that cycle times dramatically increase as you decrease temperature from 60º on the Cottons and Heavy Duty Cycles. Of course, this is likely to change if you run smaller loads, and it adjusts cycle times to compensate for each load, but here is a rough idea.
Here is what I've noted at and below 60º:
<ul>
<li>@ 60º - 1hr 45mins before machine is started</li>
<li>@ 50/40º - 2hrs 15mins</li>
<li>30º - 2hrs 30mins</li>
<li>Cold - 2hrs 45mins</li>
</ul>
These are only a rough guide, as I don't remember each cycle like I do on the dishwasher. Although, I take Miele are aware of the 4 points of washing Launderess points out frequently: Time, Temperature, Chemical and Mechanical action. Cold temperature removes chemical and temperature action (Enzymes are for the most part working best from 35º - 45 or 50º), so the Miele adds time for more mechanical action.
What I understand from your post is the washer is either taking too long without extra rinses, or takes 40 minutes by default. I am *thinking* that maybe the cold option does this? Do you know if the machine increases/decreases time as your get hotter (mine increases again after you from 60º, but only by 20mins for water heating).
I also wasn't aware of your machine being so far from the water heater. Like the others have said, running a hot wash on the machine will be equal to running a warmish wash, with the cold(ish) tub, clothes and standing water in the pipes. I agree with their suggestions on that front. If you have a recirculation system on the house you could run it before running a "Hot" wash so that you get a truly hot wash, instead of that luke-warm your house has made you put up with? (Probably one point where the Top-Loader wins: It uses so much water that running the taps hot first is not really needed!)