doesn't seem to work for me :)

my $x = *Time::HiRes::gettimeofday;
print "original: ", Time::HiRes::gettimeofday(), "\n";
# ...
*Time::HiRes::gettimeofday = sub() { $x; };
                             #  ^^ avoids "Prototype mismatch"
print "restored: ", Time::HiRes::gettimeofday(), "\n";
[download]

prints:

original: 117275763140928
restored: *Time::HiRes::gettimeofday
[download]

(i.e. after having been restored, the function prints the stringified representation of the glob $x)