I've seen voice delays of over six seconds, my best guess for delay when using the button is up to two seconds. That is speculation and likely heavily affected by ISP/router.
People who complain about not getting a check six, especially in the middle of a large furball where you should perpetually be in "check six" mode anyway are self-centered, lack SA and gay. Or maybe they're straight because they don't enjoy getting it from back there. Either way, it's moot because it'll be legal everywhere soon.
90% of people on are good at giving checks despite the fact that giving checks depends on excess time and SA. You could whine, but remember this: expecting anyone to love you more than you is setting you up for failure