@Override
        public String toString() {
            return "DelayedRefreshable{" +
                    "expireTimeWithBufferEpoch=" + LogUtil.instant(expireTimeWithBufferEpochMs) +
                    "expireTimeEpoch=" + LogUtil.instant(expireTimeWithBufferEpochMs) +
                    ", refreshable=" + refreshable +
                    '}';
        }
@return The {@link Refreshable} that spawned this {@link DelayedRefreshable}.
stroom-security/stroom-security-common-impl/src/main/java/stroom/security/common/impl/RefreshManager.java