Conference Agenda

We show that retail participation is increasingly rule-based rather than discretionary, leaving sharp and recurring intraday footprints in trading activity. Using transaction-level data from SPX zero-days-to-expiration (0DTE) options, we document pronounced volume spikes exactly at the hour and half-hour marks that emerge almost instantaneously and dissipate within seconds. These spikes intensify over time, are concentrated in complex multi-leg trades, and are largely absent in longer-dated contracts. Spike-time trading is dominated by small, standardized, short-premium strategies consistent with template-driven execution and mechanical risk budgeting, and we do not find evidence that these trades are systematically wealth-depleting. Around these deterministic windows, quoted spreads tighten while effective spreads widen, indicating intensified liquidity provision alongside higher execution costs. Overall, fintech-enabled retail automation generates synchronized order flow that reshapes intraday liquidity and market quality.