Question about AVM FRITZ!Repeater 3000 AX

It depends if you use it in pure wifi mode (fritzbox -> wifi -> 3000AX -> wifi -> PC), in which case the latency depends on the distance between the Fritzbox and the repeater, generally between 2 and 40 ms).
In LAN mode (fritzbox -> LAN GB -> 3000AX -> wifi -> PC), it's between 2 ms and <1ms, in fact like a direct wifi connection to the Fritzbox.