Do you know how their "spot pricing" works, exactly? "lets you use spare GPUs" doesn't tell us much. Is it granular to how long the duration the model is active

Do you know how their "spot pricing" works, exactly? "lets you use spare GPUs" doesn't tell us much. Is it granular to how long the duration the model is actively processing your prompt? ..or do you get dinged for an hour immediately and again on the hour?