PriNet:

You could use stat to get the file modification time, and then sit in a loop waiting for the file modification time to change:

$ cat pm_1198604.pl
use strict;
use warnings;

system("touch FName.dat");
my $ctime = (stat 'FName.dat')[10];

# Proxy for your spreadsheet update...
system("(sleep 10; date; touch FName.dat) &");

my $timeout = time + 60;    # Don't wait forever!

while (1) {

    # File changed yet?
    my $new_ctime = (stat 'FName.dat')[10];
    last if $new_ctime > $ctime;

    die "TIMEOUT!" if time > $timeout;

    print "still unchanged, waiting a little while\n";
    sleep 2;
}

print ".. continuing to next chunk of work\n";

$ perl pm_1198604.pl
still unchanged, waiting a little while
still unchanged, waiting a little while
still unchanged, waiting a little while
still unchanged, waiting a little while
still unchanged, waiting a little while
still unchanged, waiting a little while
Sun, Sep  3, 2017 11:35:11 AM
.. continuing to next chunk of work
[download]

...roboticus

When your only tool is a hammer, all problems look like your thumb.