  Context: The winter seeing at Concordia is essentially bimodal, excellent or
quite poor, with relative proportions that depend on altitude above the snow
surface. This paper studies the temporal behavior of the good seeing sequences.
Aims: An efficient exploitation of extremely good seeing with an adaptive
optics system needs long integrations. It is then important to explore the
temporal distribution of the fraction of time providing excellent seeing.
Methods: Temporal windows of good seeing are created by a simple binary
process. Good or bad. Their autocorrelations are corrected for those of the
existing data sets, since these are not continuous, being often interrupted by
technical problems in addition to the adverse weather gaps. At the end these
corrected autocorrelations provide the typical duration of good seeing
sequences. This study has to be a little detailed as its results depend on the
season, summer or winter. Results: Using a threshold of 0.5 arcsec to define
the "good seeing", three characteristic numbers are found to describe the
temporal evolution of the good seeing windows. The first number is the mean
duration of an uninterrupted good seeing sequence: it is $\tau_0=7.5$ hours at
8 m above the ground (15 hours at 20 m). These sequences are randomly
distributed in time, with a negative exponential law of damping time
$\tau_1=29$ hours (at elevation 8 m and 20 m). The third number is the mean
time between two 29 hours episodes. It is T=10 days at 8 m high (5 days at 20
m).
