My current route is...

library(data.table)
IDateTime(as.POSIXct("20171002095500", format = "%Y%m%d%H%M%S"))

#         idate    itime
# 1: 2017-10-02 09:55:00

but it would be nice to directly do IDateTime("20171002095500", format = "%Y%m%d%H%M%S") since my approach seems hacky and I am wary of POSIXct getting up to timezone shenanigans that I have no interest in.