Clarified behavior of "24:00:00" in as.ITime() (#7057)

Author: venom1204

DESCRIPTION

@@ -102,5 +102,6 @@ Authors@R: c(
   person("Aljaž", "Sluga",         role="ctb"),
   person("Bill", "Evans",          role="ctb"),
   person("Reino", "Bruner",        role="ctb"),
-  person(comment=c(github="@badasahog"), role="ctb")
+  person(comment=c(github="@badasahog"), role="ctb"),
+  person("Vinit", "Thakur",        role="ctb")
   )

man/IDateTime.Rd

@@ -137,6 +137,11 @@ hours. Because \code{ITime} is stored in seconds, you can add it to a
 \code{POSIXct} object, but you should not add it to a \code{Date}
 object.
 
+For \code{as.ITime}, note that the string \code{"24:00:00"} is parsed as \code{"00:00:00"}.
+This is because the conversion uses \code{as.POSIXct}, which treats \code{"24:00:00"} as midnight of the next day. 
+This differs from ISO 8601 (which allows \code{"24:00:00"} to represent end-of-day), but aligns with POSIX standards.
+To represent end-of-day intervals, use \code{"23:59:59"} or arithmetic (e.g., \code{as.ITime("23:59:59") + 1L}).
+
 We also provide S3 methods to convert to and from \code{Date} and \code{POSIXct}.
 
 \code{ITime} is time zone-agnostic. When converting \code{ITime} and
@@ -245,6 +250,12 @@ identical(as.ITime("10:45"), methods::as("10:45", "ITime"))
 
 (t <- as.ITime("10:45:04", format = "\%H:\%M:\%S"))
 
+# "24:00:00" is parsed as "00:00:00"
+as.ITime("24:00:00")
+
+# Workaround for end-of-day: add 1 second to "23:59:59"
+as.ITime("23:59:59") + 1L
+
 as.POSIXct("2001-01-01") + as.ITime("10:45")
 
 datetime <- seq(as.POSIXct("2001-01-01"), as.POSIXct("2001-01-03"), by = "5 hour")