Also I beat DDS in 25 hours and DDS2 in 20 hours. I spent an extra 10 or so hours on both for optional bosses. I don't know if your 30-40 hour estimate is including them (and starting NG+ maybe), but if not that's generous.
The 30-40 hours is including optional bosses and mastering all the mantras.
*edit* Specifically since according to how long to beat, the average person is slow at completing games whether it's their first time or not. The time it takes for me to complete everything on some games is sometimes less than it takes for the main game on HLTB. I've most recently played Suikoden so I'll use that as an example, but I haven't played it in years and during my current playthrough, varied my party with new characters every single area so didn't use the same few the entire game, got 108 stars although didn't revive Gremio because I was too late to get Leon so had to wait until after the last war battle, and I still got 10:15 while HLTB's average is 22 hours for the main story. This is with player statistics of over 200. The main story "rushed" statistic is 19 hours, and the speed run statistic is 12 hours. I certainly didn't attempt a speed run and finished the game faster.
So yeah, my time I listed on DDS was a little generous 30 hours being only five more than what you listed, but based it on a complete playthrough because imo, the average person completes games pretty slow when comparing times on games at places like HLTB.