Rollover time is the specific moment each trading day (commonly 5pm New York time, aligned with the shift from one settlement date to the next) when open positions are marked for the daily swap charge or credit. Positions still open at that instant are charged the overnight interest-rate differential for holding the trade one more day.
Brokers typically apply a triple swap charge on Wednesdays to account for the weekend, since the standard T+2 settlement means Wednesday's rollover effectively covers three calendar days of interest.
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The Best Time to Trade Forex
A hub over the four sessions and the overlaps: when liquidity is actually there, why cost follows it, and why the calendar beats the clock.