How is the query response system structured?

Question

Node.js

I send requests from the node, in the amount of 5 pieces. The difference in responses floats from 50 to 200 ms, and the response comes earlier, far from the first request sent. Why is this happening? Requests are all exactly the same, POST.
I also want to ask in addition:
I sent requests with a different api key + code (this is required by the site) and for some reason from two different accounts the site responded to one of them faster (what could this be connected with?)