The ACK delay timer is a fixed timeout, classically about 100ms. It was put in to piggyback ACKs of echoed characters on the echoed character packet, for use with TELNET. So it's a human-scaled delay. It's not a function of round trip time.

It's hard to turn off. There's the socket option TCP_QUICKACK, but you have to reset it on every "recv" call on Linux. For Windows, see SIO_TCP_SET_ACK_FREQUENCY.

For a multiplayer game, you usually control both client and server, so you can set this at both ends. It improves performance when set at the other end, so if you only have control of one end, it's not that helpful.

Anyway, try it, and do something like fast remote procedure calls to test.