I just went went through my 1st Regen today, but @diesel is correct, there appears to be a "pre-Regen" that lasts for about a minute where the MAP drops below 14 on the Scan Gauge ( at least mine did) before the actual Regen starts ( #1 on my Scan Gauge 2) . This could be the point at which the DPF is getting flooded with fuel and the the DPF is heating up because once the actual Regen starts ( #1 in the gauge) , the Soot Mass starts to drop pretty quickly.
Bump for for update to this thread: Since I @GlennGlenn get the frequent regens at less than 60 miles between regens since firmware reflash at dealer two months ago, I've become somewhat "quite" familiar with regens, seeing two-three a day. Dealer says this is normal and to be expected.
Just before a regen, you will see the Map go below / less than 14 on the SC2. This is the period when you do not want to turn off your CTD. It's not in pre-regen long, perhaps two minutes or less, but it is setting the system up for the actual regen which is indicated on the SC2 as #1. If you interrupt the pre-regen , you'll get a #3 on the sc2 and this is not good. Interrupting the #1 is fine as the car will just start regen mode once it gets to temp. You do not want to unterript the preregen that is just before the SC2 goes to #1.