Are you looking for something like this?
library(lubridate)
DF <- data.frame(Time = seq.Date(from = as.Date("2018-05-01"),
to = as.Date("2019-03-31"), by = 1),
Volume = rnorm(n = 335, 1000000, 200000))
Months = as.Date("2018-05-01") %m+% months(0:10)
Labels <- format(Months, "%Y-%b")
plot(DF$Time, DF$Volume, xaxt = "n")
axis(1, at = Months, labels = Labels)

Created on 2020-06-06 by the reprex package (v0.3.0)