It makes a bit more difference if you factor in compile time (more tokens to parse, and no optimization of multiplying constants, don't ask me which makes more of a difference):

use strict;
use warnings;

use Benchmark;
my $x = 5;

timethese(-5, {
 EXPANDED=>sub { eval '$x * 24 * 60 * 60' },
 NOT_EXP =>sub { eval '$x * 86400' },
});

Benchmark: running EXPANDED, NOT_EXP, each for at least 5 CPU seconds.
+..
  EXPANDED:  6 wallclock secs ( 5.31 usr +  0.00 sys =  5.31 CPU) @ 56
+77.40/s (n
=30147)
   NOT_EXP:  6 wallclock secs ( 5.26 usr +  0.00 sys =  5.26 CPU) @ 67
+49.24/s (n
=35501)
[download]

But of course I'd leave in the explicit multiplications anyway for reasons already mentioned. If I really needed to eval that, I might put something like $seconds_per_day = 24 * 60 * 60; outside of the eval, then use the variable inside.