@murch They’re all block timestamps; i don’t care how or when they get mined - someone shouldn’t be able to construct a valid chain with a higher blockrate (in terms of stated timestamps) on average than 1 per 10 minutes unless they increase the difficulty.
The first period takes ~2.83 weeks, so difficulty goes to D/\sqrt{2} in the second period. The second period takes the same amount of time, so the difficulty drops to D/2 in the third period. After the third period the difficulty doubles again (due to the maximum difficulty adjustment of 2x upwards in this scenario), so back to D.