SPY 1-minute volume averages 251K shares at 09:30 and 277K at 15:55 — but only 57K at 12:30. Volume and range concentrate at open and close, and that's exactly where manual route control matters most. Smart routers work the middle.

Dark pools are not a magic edge. FINRA data shows off-exchange flow splits between ATS dark venues and non-ATS wholesalers, and the mix is symbol-specific. The desk routes dark only when footprint or midpoint interaction beats immediacy.