An instant is a specific moment in time. Most common date-time objects (e.g, POSIXct, POSIXlt, and Date objects) are instants.
is.instant(x)
is.timepoint(x)
an R object
TRUE if x is a POSIXct, POSIXlt, or Date object, FALSE otherwise.
is.instant(as.Date("2009-08-03")) # TRUE
#> [1] TRUE
is.timepoint(5) # FALSE
#> [1] FALSE