set title "Fsteps plot\nwith date and time as x-values"
set data style fsteps
set xlabel "Date\nTime"
set timefmt "%d/%m/%y\t%H%M"
set yrange [ 0 : ]
set xdata time
set xrange [ "1/6/93":"1/11/93" ]
set ylabel "Concentration\nmg/l"
set format x "%d/%m\n%H:%M"
set grid
set key left
plot 'timedat.dat' using 1:3 t '' \
, 'timedat.dat' using 1:3 t 'Total P' with points \
, 'timedat.dat' using 1:4 t '' \
, 'timedat.dat' using 1:4 t 'PO4' with points 
pause -1 'Test <Return> '
reset