Plotting times with hours and minutes

May be something like this:

dataset <- read.table(text = 'time  avg_holds month
0:00      1.15  June 
0:15      0.396 June 
0:30      0     June 
0:45      4.76  June 
1:00      1.59  June 
1:15      0     June 
1:30      0     June 
1:45      0     June 
10:00     2.19  June 
10:15     3.65  June',
                     header = TRUE,
                     stringsAsFactors = FALSE)

with(data = dataset,
     expr =
       {
         time = as.POSIXct(x = time,
                           format = "%H:%M") # assuming 24 hour time format
         plot(x = time,
              y = avg_holds)
       })

Created on 2019-08-19 by the reprex package (v0.3.0)