f(n) := if n < 2 then n else f(n - 1) + f(n - 2)$

/* First solution, call the time function with an output line number, it gives the time taken to compute that line.
   Here it's assumed to be %o2 */
f(24);
46368

time(%o2);
[0.99]

/* Second solution, change a system flag to print timings for all following lines */
showtime: true$

f(24);
Evaluation took 0.9400 seconds (0.9400 elapsed)
46368