Pausing ACS?

In addition, I'd recommend checking out https://zdoom.org/wiki/TagWait - this function will cause the script to pause until the tagged sector has stopped moving. Depending on the effect you're trying to achieve, it can be a lot easier to use and lower maintenance.

Check out https://zdoom.org/wiki/Delay

 #include "zcommon.acs"

script 1 (void)
{
    Ceiling_RaiseByValue(first one);
    delay (35*needed_seconds);
    Thing_Spawn(first chaingunner);
		delay (35*needed seconds);
    Ceiling_RaiseByValue(second one);
    delay (35*needed_seconds);
    Thing_Spawn(second one);
		delay (35*needed seconds);
    Ceiling_RaiseByValue(third one);
    delay (35*needed_seconds);
    Thing_Spawn(third one);   
} 

35 means "35 tics (read as "1 second"). Some people do 36 instead of 35, because "read the wiki". Anyway, quick maths. 35 * 3 = 3 seconds. 35 * 10 = 10 seconds

Thanks to everyone who helped me, and @skillsaw, your comment was very helpful!