Plotting a Histogram of Time Values where the x-axis ranges from 17:30 to 7:30

I have made this question a reproducible example. Here is a portion of my data frame:

df <- structure(list(`Room Out Date` = c("2018-07-08", "2018-07-08", 
                "2018-07-08", "2018-07-09", "2018-07-09", "2018-07-09", "2018-07-09", 
                "2018-07-09", "2018-07-09", "2018-07-09", "2018-07-09", "2018-07-09", 
                "2018-07-10", "2018-07-10", "2018-07-10"), 
                `Room Out Time` = c("20:11:00", 
                "20:43:00", "22:28:00", "18:00:00", "18:32:00", "18:40:00", "18:59:00", 
                "19:16:00", "19:22:00", "19:38:00", "19:48:00", "21:24:00", "18:12:00", 
                "18:38:00", "18:40:00")), row.names = c(NA, -15L), 
                class = c("tbl_df", "tbl", "data.frame"))

I would like to create a histogram with times on the x-axis ranging from 17:30 to 07:30 (with a binwidth of 30 minutes) and count on the y-axis. I have tried converting the times using the chron library as well as with posixct, but ggplot doesn't seem to like either of those methods. Any help is much appreciated.

Solution

Edited: Now collating all dates by half hour period

Try lubridate:

library(lubridate)

df %>%
  mutate(fakedate = ymd("2000-01-01")) %>%  # pretend all happen on same day
  mutate(fakedate_time = as_datetime(paste(fakedate, `Room Out Time`))) %>% 
  mutate(fakedate_time = as_datetime(ifelse(fakedate_time > as_datetime("2000-01-01 12:00:00"),
                                            fakedate_time,
                                            fakedate_time + days(1)))) %>%  # promote some to after midnight
  ggplot(aes(fakedate_time)) +
  geom_histogram(binwidth = 1800) +  # bins of 1800 seconds = 30 minutes
  xlim(as_datetime("2000-01-01 17:00:00"), as_datetime("2000-01-02 07:30:00"))