OK, I emailed Briess about their Pils extracts and got a response on the long boil question. Since I use it in 30 minute boils regularly to try hops (and heard anecdotes here about even shorter boils) and never gotten DMS, I expected something along these lines :
"Hi Jon,
Thanks for getting in touch.
In general, our extracts are boiled gently and then evaporated. Both of these processes will drive off DMS. We essentially use a large brewing system, and of course the malt and process will be a bit different each time. If you boil the DME at all, you should be left with no excess DMS, as this is the second time this pilsen malt has been boiled. So no, 90 minutes isn't necessary.
Regards,
Aaron Hyde
Homebrew Products Manager
Briess Malt & Ingredients Co."