measure execution time in linux

So I'm doing a quality assurance task with raspberry pi under linux, the 7 programs are preload, preload.c,run_test, run_test.c, runit_mainain,runit_preload,runit_test.

What I do is running runit_preload,and then run run_test, and then unplug the raspberry and at last run runit_maintain. I need to record the time of the execution time of each program but every time I try time -p runit_preload or time -p ./preload.c,it never shows the time but instead runs the program again.