[R] axis command and excel time format

[Carmen Meier]

Hi to all,
I have some problems to get the times-scale to the x-axis the times are 
coming from an excel sheet f. e
[1] "0:01:00" "0:02:00" "0:03:00" "0:04:00" "0:05:00" "0:06:00" "0:07:00"
 [8] "0:08:00" "0:09:00" "0:10:00" "0:11:00" "0:12:00" "0:13:00" "0:14:00"
[15] "0:15:00" "0:16:00" "0:17:00" "0:18:00" "0:19:00" "0:20:00" "0:21:00"
[22] "0:22:00" "0:23:00" "0:24:00" "0:25:00" "0:26:00" "0:27:00" "0:28:00"
[29] "0:29:00" "0:30:00" "0:31:00" "0:32:00" "0:33:00" "0:34:00" "0:35:00"
[36] "0:36:00" "0:37:00" "0:38:00" "0:39:00" "0:40:00" "0:41:00" "0:42:00"
[43] "0:43:00" "0:44:00" "0:45:00" "0:46:00" "0:47:00" "0:48:00" "0:49:00"
[50] "0:50:00"

I found the solution from tread 
http://finzi.psych.upenn.edu/R/Rhelp02a/archive/71234.html
with an very good result:
/> ># test data /
/> >tt <- c("23:05:02", "23:10:02", "23:15:03", "23:20:03", "23:25:03", /
/> >"23:30:03", "23:35:03", "23:40:03", "23:45:04", "23:50:04", 
"23:55:03", /
/> >"23:55:03") /
/> >x <- c(0.575764, 0.738379, 0.567414, 0.663436, 0.599834, 0.679571, /
/> >0.88141, 0.868848, 0.969271, 0.878968, 0.990972, 0.990972) /
/> > /
/> >library(zoo) /
/> >library(chron) /
/> >z <- zoo(x, times(tt)) /
/> >plot(z) /
/> > /
but I am unable to use the axis command for that issue:
how could I change the      axis(1, xaxp=c(0,50,5),font=2)  that I will 
get a changeable amount of x-axis entries with a time format hr:min

    par(cex=1.2,lwd=1)
    range(x <- c(0,50))
    range(y <- c(0,10))
    plot(x,y, type="n",adj=0, asp=0, xlab="", 
ylab="",axes=FALSE,font.axis=2)
   axis(1, xaxp=c(0,50,5),font=2)
    axis(2, 0:10,font=2)
    box()



Thank`s in advance

Carmen