Core-to-RAM latency is in the neighborhood of 50 ns (well-tuned Intel system with low-latency memory) to ~80 ns (bottom-of-the-barrel system). At propagation speed, that's about 10 meters. A big chunk of this latency is internal to the CPU (so is not influenced by distance to the memory at all), another big chunk is the inherent slowness of accessing a DRAM array (10+ ns, independent of the location of the memory).

It's worth pointing out how little this has changed over the past decades. A 2006 AMD CPU is 100 % competitive in regards to memory latency with Intel's 2020 flagship desktop CPU.