As I repeatedly forgot how to convert Excel dates to POSIX here's the specific function.
Usage
XLDateToPOSIXct(x, tz = "GMT")
Arguments
x
the integer vector to be converted.
tz
a time zone specification to be used for the conversion, if one is required. See as.POSIXct.
Value
return an object of the class POSIXct. Date-times known to be invalid will be returned as NA.
Details
XLGetRange will return dates as integer values, because XL stores them as integers. An Excel date can be converted with the (unusual) origin of
as.Date(myDate, origin="1899-12-30"), which is implemented here.