  In this paper we describe the method of measurement of optical turbulence in
twilight with MASS-DIMM. Some results of such observations carried out with SAI
ASM installed on Mt. Shatdzatmaz: 1) characteristics of optical turbulence
don't change significantly in transition between day and night 2) twilight
measurements of seeing can be used for selection of observational program for
big telescope on condition that program switching is long - longer than 30-40
minutes. In conclusions we list upgrades of ASM system needed to improve
capabilities to observe on twilight.
