Yes this one works, but (sorry) in the OP there was a plot without data
to define the range
So I tried to use your working suggestion in that manner:

library(zoo)
library(chron)
time <-
c("2:25:00","2:26:00","2:27:00","2:28:00","2:29:00","2:30:00","2:31:00",
   
"2:32:00","2:33:00","2:34:00","2:35:00","2:36:00","2:37:00","2:38:00",
     
"2:39:00","2:40:00","2:41:00","2:42:00","2:43:00","2:44:00","2:45:00",
   
"2:46:00","2:47:00","2:48:00","2:49:00","2:50:00","2:51:00","2:52:00",
     
"2:53:00","2:54:00","2:55:00","2:56:00","2:57:00","2:58:00","2:59:00",
     
"3:00:00","3:01:00","3:02:00","3:03:00","3:04:00","3:05:00","3:06:00",
     
"3:07:00","3:08:00","3:09:00","3:10:00","3:11:00","3:12:00","3:13:00",
      "3:14:00")
  min_time <- min(times(time))
  max_time <- max(times(time))

  duration <- max_time-min_time
   h <- hours(duration) # not nessesary here
  m <- minutes(duration)
  par(cex=1.2,lwd=1)
  range(x <- c(0,m)) #50 minutes
  range(y <- c(0,10))
  plot(x,y, type="n",adj=0, asp=0, xlab="",
ylab="",axes=FALSE,font.axis=2)
#   axis(1, 0:m,font=2) # works fine but not with times

#---------- your suggestion --------
mn <- times(min_time)
mx <- times(max_time)
n <- 5

xt <- times(seq(mn, mx, length = n))

xt <- times(unique(sub("..$", "00", xt)))

axis(1, xt, sub(":00$", "", xt)) # works only with plot data before
#----------------------
  axis(2, 0:10,font=2)
  box()


Maybe you could explain the difference

Best regards Carmen

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