if we go to any thread we have an option ro delay thread creation until needed.We can click this option if we dont want to add users until we actually need them for execution. We have another option below that called schedular. If we click it then we have option of the time i.e at what time we want to add that thread to our test.If we put any time like 5 minutes late than present time then that thread will be add 5 minutes after only.We can even add the end time i.e what we want the total duration of our thread to be.

We can even add startup delay in seconds and duration as well.But please note if we add these two options it will override the above two options.i,e if we add delay of 5 secs then no matter even if the start up time is after 10 mins the thread will start after 5 secs and if the duration of thread is 20 secs then if the difference between start up time and end time is 5 mins,the thread will end after 20 secs.

But also note if we have put a ramp up period of let us say 10 secs that it will override the duration and all users will be added in 10 secs.If we have not added the ramp up i.e it is 1 sec period then all users will be added in 1 sec.If ramp up is 30 and duration is 20 then users will be added in 30 secs.