I usually read instantaneous values for the depth - I wear a Perdix, a Suunto HelO2 and sometimes a D6i also and their readings change simultaneously.
I never changed the default sample rate that is what recorded in the log. I can also say that, the max depth, even if recorded in the summary, sometimes it is not reported in the log because did not occurred during a sample period, but just for very limited time.
For what concerns the temperature reading, I never put much focus on its speed, but, because it always took some times to adjust when entering into the water, I ascribe it to inertia due to the mass surrounding the temperature sensor. So it will always be delayed regardless the measuring rate.
Anyway, I don't think it's so important to know the exact time when the temperature reached that value, isn't it ?