i've found my beers are good after about 6 weeks of conditioning... bottled. but again, ymmv.

DMS is created from form the precurser called SMM, This is found in higher quantities in Pilsner malt, The stronger the boil and the boil time will determine how much of this precurser is boiled off. However boil time is not the only concern. The speed at which the wort is chilled below 140F also has an effect. The faster you can cool it the less likely you will end up with SMM in your wort.

The boil 90 minute thing is not an exact science...it more has to do with half lifes...say every 10 minutes of boil time you reduce the amount of SMM by half...so you atart at 100 then after 10 minutes you have 50 left after another 10 you have 25 left..They chose 90 minutes because after that amount of time the amount left over is so small it will not be noticeable. It also depends on the amount of pilsner malt in your recipe...if this is a 100% pilsner malt beer you better be boiling for at least 90 minutes...or be prepared to drink some rotting vegetables...if you have 30-50% Pilsner malt you may not need the full 90 minutes...The 90 minutes is not a definitive number but it a number that should work most of the time(assuming your other processes are sound).

Not seeing much activity after 2 days, should I be worried?

Not necessarily. It can sometimes take a few days for the yeast to ramp up. Also, sometimes there aren't a lot of visible signs of activity. Sometimes, there's little or no krausen on top, and if you're using a fermenter with an airlock, there may be little or no noticeable airlock activity.

Check for trub (sediment on the bottom) formation. If you've got trub, you've got fermentation.

Ok great, there is a good bit of trub so that's good to know!

The Patersbier recipe I've seen sounds pretty similar - 100% pilsner and a 60 min boil. And since the recipe is from two (what I would say) very advanced brewers, I'm convinced the 60 min boil is more than OK.