Reliable way to get remaining DataStore requests?

From what I've read on the wiki, something like this should work:

local Requests

while wait(60) do
    local NumPlayers = game:GetService("Players").NumPlayers
    Requests = Requests + (60 + (10 * NumPlayers))
end

But it doesn't. My save system still messes up at times. I think the issue is that the requests don't add up on a fixed cycle (exactly every minute). So, my questions are: When do normal requests get added from the server? Is it one time per second? When do the per-player requests get added? Is it every 6 seconds from that they have entered until they leave? OR, is everything added on a fixed cycle and I'm just doing it wrong? I am slightly confused, and I don't want to risk messing up the data for my game so any answer is appreciated. Thanks.