private static Instant getEarliestRetainedCreateTime(final DataRetentionRule rule, Instant now) {
        return DataRetentionCreationTimeUtil.minus(now, rule);
    }
Gets the earliest meta create time that would be retained by this rule.
stroom-data/stroom-data-retention-impl/src/main/java/stroom/data/retention/impl/DataRetentionPolicyExecutor.java