Rollover hour
The hour each trading day when open positions are charged or credited swap, and spreads typically widen.
Once a day, usually around the New York close, brokers apply the daily swap charge for holding positions overnight and briefly widen their spreads while liquidity thins out.
A signal history with many entries clustered in that hour is a history that is harder for a subscriber to copy at the published cost, since the price actually available at that moment is usually worse than the rest of the day’s.