Please see my answer inline. In my case, the nb of users is almost the same all day, does that mean I > have to put "1" for the ramp-up period ? > If the machine running jmeter is not good enough, 500 thread cannot be started in 1 second. Are you ok if it's not 500 concurrent thread at 1st sec?
Also how can I simulate a test day during 8 hours? Is the scheduler (with > start time and end time) useful for that ? > If you'd like to test for 8 hour and 1 time, it's ok to use jmeter scheduler. If you'd like to run some kind of longevity test for few days, you may need to consider OS scheduler to execute the script daily. How do I set my script to set up 10 operations per user per hour ? > Throughput Controller should fit your requirement http://jmeter.apache.org/usermanual/component_reference.html#Throughput_Controller
