R字符到日期时间导致不适用

Question

是的，我发现了很多方法

但是对我来说，没有办法。

我有一个csv文件，我将其读入R

Week <- read.csv(file="week.csv", header=TRUE, sep=",", stringsAsFactors = FALSE)

我试图将StartTime和EndTime转换为datetime（例如：2019-01-04 15:13:07）

我尝试了这些方法

Week <- read.csv(file="week.csv", header=TRUE, sep=",", stringsAsFactors = FALSE)%>%
              mutate(StartTime = as.POSIXct(StartTime, format = "%Y-%m-%d %H:%M:%S"))

和

Week$StartTime <- setDT(Week)[,ymd_hms(Week$StartTime)]

和

Week$StartTime <- as.POSIXct(Week$StartTime, format = "%Y-%m-%d %H:%M:%S")

但是都返回NA

我不知道还能做什么。

附加文件，希望有人可以帮助我。

https://drive.google.com/open?id=1qIOWkoVwlMu-Y6GZ_Nu0WqlcFRzyTO2v

谢谢

补充文字：

library(data.table)
Week=data.table(First=c("sat","sun","sat","sun","sat","sun","sat","sun","holiday"),
                StartTime=c("2018-09-01 00:00:00","2018-09-02 00:00:00","2018-09-08 00:00:00","2018-09-09 00:00:00","2018-09-15 00:00:00","2018-09-16 00:00:00","2018-09-22 00:00:00","2018-09-23 00:00:00","2018-09-24 00:00:00"),
                EndTime=c("2018-09-01 23:59:59","2018-09-02 23:59:59","2018-09-08 23:59:59","2018-09-09 23:59:59","2018-09-15 23:59:59","2018-09-16 23:59:59","2018-09-22 23:59:59","2018-09-23 23:59:59","2018-09-24 23:59:59"))