Sys.Date returns the system's idea of the
current date with and without time.
Sys.time returns an object of class
DateTimeClasses). On almost all systems it will have
sub-second accuracy, possibly microseconds or better. On Windows it
increments in clock ticks (usually 1/60 of a second) reported to
Sys.Date returns an object of class
"Date" (see Date).
Sys.time returns an absolute date-time value which can be
converted to various time zones and may return different days.
Sys.Date returns the current day in the current time zone.
date for the system time in a fixed-format character
system.time for measuring elapsed/CPU time of expressions.