  The variability of active galactic nuclei (AGNs) is ubiquitous but has not
yet been understood. Measuring the optical variation properties of AGNs, such
as variation timescale and amplitude, and then correlating them with their
fundamental physical parameters, have long served as a critical way of
exploring the origin of AGN variability and the associated physics of the
accretion process in AGNs. Obtaining accurate variation properties of AGNs is
thus essential. It has been found that the damped random walk (DRW) process can
well describe the AGN optical variation, however, there is a controversy over
how long a minimal monitoring baseline is required to obtain unbiased variation
properties. In this work, we settle the controversy by exhaustively
scrutinizing the complex combination of assumed priors, adopted best-fit
values, ensemble averaging methods, and fitting methods. Then, the newly
proposed is an optimized solution where unbiased variation properties of an AGN
sample possessing the same variation timescale can be obtained with a minimal
baseline of about 10 times their variation timescale. Finally, the new
optimized solution is used to demonstrate the positive role of time domain
surveys to be conducted by the Wide Field Survey Telescope in improving
constraints on AGN variation properties.
