How to control xticks in multiplot mode - plot

Question

As the title says, I want to find a way to control the xtics in multiplot mode. The output is the following
The plots shown in the first two rows are OK. However, the following three suffer from the very same problem. The numbers on the x axes are very close to each other and in some cases overlapping. So, is there a way to fix this? All input is read from external data files and I cannot know beforehand what is the maximum value of t so as to set xrange [0:max] in every plot and then control the xtics. By the way, is it possible in gnuplot to read the external data file before the plot stage and define the maximum value of t in each plot?
Many thanks in advance.
EDIT
The script used to produce the above output is the following:
reset
set term postscript eps enhanced "Helvetica" 20 size 7in, 11in
set output 'plots.eps'
set size 1,1
set multiplot layout 4, 2
unset key
# plotting the time-evolution of the mLCN
set xrange [*:*]
set xlabel 't'
set ylabel 'mLCN'
plot "hh.rli" u 1:3 w l lc rgb 'black'
# plotting the time-evolution of the RLI
set xrange [*:*]
set xlabel 't'
set ylabel 'log(RLI)'
plot "hh.rli" u 1:(log10($2)) w l lc rgb 'black'
# plotting the time-evolution of the FLI
set xrange [*:*]
set xlabel 't'
set ylabel 'log(FLI)'
plot "hh.fli" u 1:(log10($2)) w l lc rgb 'black'
# plotting the time-evolution of the OFLI
set xrange [*:*]
set xlabel 't'
set ylabel 'log(OFLI)'
plot "hh.fli" u 1:(log10($3)) w l lc rgb 'black'
# plotting the time-evolution of the SALI
set xrange [*:*]
set xlabel 't'
set ylabel 'log(SALI)'
plot "hh.sali" u 1:(log10($2)) w l lc rgb 'black'
# plotting the time-evolution of the GALIs
set xrange [*:*]
set xlabel 't'
set ylabel 'log(GALIs)'
plot "hh.gali" u 1:(log10($2)) w l lt 1 lc rgb 'green',\
"hh.gali" u 1:(log10($3)) w l lt 1 lc rgb 'red',\
"hh.gali" u 1:(log10($4)) w l lt 1 lc rgb 'blue'
# plotting the time-evolution of the MEGNO
set xrange [*:*]
set xlabel 't'
set ylabel 'MEGNO'
plot "hh.megno" u 1:2 w l lc rgb 'black'
# plotting the time-evolution of the Spectral Distance (D)
set xrange [*:*]
set yrange [-0.1:4]
set xlabel 't'
set ylabel 'D'
plot "hh.sd" u 1:2 w l lc rgb 'black'
unset multiplot
reset
set terminal windows
quit

Answer 1

You can tell gnuplot to rotate the tick labels with:
set xtics rotate
That'll take more vertical space, though. You can probably find a compromise solution by picking an angle less than 90 degrees with:
set xtics rotate by 45
or whatever angle looks best.

Answer 2

You can try increasing the distance between individual tics. For example, in the bottom left corner plot, instead of showing every 500th tic, you may show every 1000th. This can be easily achieved by using
set xtics 1000