What is a good round-trip latency for recording?

Single-digit milliseconds at a 64-sample buffer is good; 2–6ms is the modern bar for a desktop interface. Round-trip includes converter and driver overhead, so it always exceeds the raw buffer math (64 samples at 48kHz ≈ 1.3ms per side). Below ~10ms most performers stop noticing; above it, timing feel degrades. And if your interface offers direct monitoring, tracking latency stops mattering at all for vocals and voice-over.