Date
Dates are 32-bit signed ints representing the number of days since the birth of 
Christ.  Negative values represent B.C.E. dates.

CDateStruct         Class class CDateStruct
DayOfWeek           Funct Day of week, given 32-bit day since AD 0.
FirstDayOfMon       Funct First day of month, given 32-bit day since AD 0.
FirstDayOfYear      Funct First day of year, given 32-bit day since AD 0.
LastDayOfMon        Funct Last day of month, given 32-bit day since AD 0.
LastDayOfYear       Funct Last day of year, given 32-bit day since AD 0.
YearStartDate       Funct 32-bit day since AD 0, given year number.
mon_start_days1     GlbVar U16 mon_start_days1[12]={
mon_start_days2     GlbVar U16 mon_start_days2[12]={


                                   
Date/CDate
TempleOS uses a 64-bit value, CDate, for date/time.  The upper 32-bits are the 
days since Christ.  The lower 32-bits store time of day divided by 4 billion 
which works out to 49710ths of a second.  You can subtract two CDate's to get a 
time span.

Use CDATE_FREQ to convert.

CDate               Class I64 class CDate
CDateStruct         Class class CDateStruct
Date2Struct         Funct Cvt CDate to CDateStruct.
Now                 Funct Current datetime.
Str2Date            Funct "*+nnnn", "*-nnnn", "mm/dd", "mm/dd/yy"
Struct2Date         Funct Cvt CDateStruct to CDate.
local_time_offset   GlbVar CDate local_time_offset;