Top panel: kinematic (nebular) ages derived from the interpolated Blöcker tracks (without the 0.546 M_⊙ model) for the point (i) when the star reaches 20 kK (lower solid line) and (ii) when the star has faded by a factor of 10 in luminosity (upper solid line). The dashed lines show the 10 kyr age when the nebula is assumed to become optically thin, and the 5 kyr age corresponds to the size limit of the HST-selected sample of 5 arcsec. The hashed area defines the visibility time of a bright PN. Lower panel: corresponding visibility time. The long-dashed (green) line shows the visibility time for the 10 kyr limit. The dashed (blue) line shows the visibility time for the HST-selected sample (5 kyr limit). The solid line shows the same but for the accelerated tracks.