Installing time can be done with:
sudo apt-get install time
Now you can time your script executions with
/usr/bin/time -v [TASKHERE]
Example to get size of the var directory
/usr/bin/time -v du -sh /var
1.2G /var Command being timed: "du -sh /var" User time (seconds): 0.01 System time (seconds): 0.06 Percent of CPU this job got: 26% Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.31 Average shared text size (kbytes): 0 Average unshared data size (kbytes): 0 Average stack size (kbytes): 0 Average total size (kbytes): 0 Maximum resident set size (kbytes): 3000 Average resident set size (kbytes): 0 Major (requiring I/O) page faults: 0 Minor (reclaiming a frame) page faults: 387 Voluntary context switches: 8227 Involuntary context switches: 3 Swaps: 0 File system inputs: 0 File system outputs: 0 Socket messages sent: 0 Socket messages received: 0 Signals delivered: 0 Page size (bytes): 4096 Exit status: 0
Giving you many types of timings for the task.