OPHLIMTI is the parameter for OPTMODE=HAS that sets the normalization for the time offset from the limits of when a source is up. The equations for the weights for rise and set are:
RISEWT=MAX(0.0,OPHLIMWT(JSCN)*(1.0-ABS(HA1(JSCN,RSTA)-HAMIN(JSCN))* 3600.0/OPHLIMTI(JSCN))) SETWT=MAX(0.0,OPHLIMWT(JSCN)*(1.0-ABS(HA1(JSCN,RSTA)-HAMAX(JSCN))* 3600.0/OPHLIMTI(JSCN)))where HA1 is the hour angle of the proposed scan, HAMIN and HAMAX are the hour angles at which the source rises or sets. This only worries about the rise and set times. Some day it maybe should also worry about experiment start and end.
See the discussion of the possible optimization modes in the section on OPTMODE for more information on OPTMODE=HAS