awaitility/src/main/java/org/awaitility/Duration.java
public Duration plus(long amount) {
        return new Plus().apply(this, unit == null ? FOREVER : new Duration(amount, unit));
    }
public Duration plus(long amount) {
        return new Plus().apply(this, unit == null ? FOREVER : new Duration(amount, unit));
    }
Add a amount (with the same time unit as the current duration)

@param amount The amount to add
@return A new amount