Gnuplot: 3D graph

set xlabel "Date"
set ylabel "Time"
set zlabel "Connections"

set xtics 86400
set ytics 14400, 14400, 86400

set xdata time
set ydata time

set format x "%m/%d/%y"
set format y "%H:%M"

set timefmt x "%m/%d/%y"
set timefmt y "%H:%M"

set dgrid3d 30,30

splot \
"blah" using 1:2:3 with pm3d, \
15 with lines lt 9