df <- data.frame(date.time = c("Fri 00:00", "Fri 23:30", "Mon 00:00", "Mon 23:30", "Sat 00:00", "Sat 23:30", "Sun 00:00", "Sun 23:30", "Thu 00:00", "Thu 23:30", "Tue 00:00", "Tue 23:30", "Wed 00:00", "Wed 23:30"), Price = c(36.15368, 41.61206, 30.80412, 37.47360, 38.04516, 35.72798, 33.05613, 32.65447, 35.50335, 41.81241, 35.14006, 37.56432, 35.04553, 38.00721))

my.order <- c(7,8,3,4,11,12,13,14,9,10,1,2,5,6)
df %>% ggplot(aes(x = reorder(date.time, my.order), y = Price, group = 1)) + geom_line()

df %>% ggplot(aes(x = reorder(date.time, my.order), y = Price, group = 1)) + geom_line() + scale_x_discrete(name = 'Day', breaks = df$date.time[c(1,3,5,7,9,11,13)], labels = c("Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"))