reqTimeMinute := reqStartTime.Truncate(time.Minute)
	if reqTimeMinute.After(h.currentMinute.statsTime) {
		// Drop the last full minute now, since we got a request for a time we
		// are not yet tracking.
		h.updateLastFullMinute(reqTimeMinute)
	}
	var entry *serviceRTTMinuteStats
	switch {
	case reqTimeMinute.Equal(h.currentMinute.statsTime):
		entry = &h.currentMinute

	// are valid).
	for _, param := range validKeys {
		paramEnvName := getEnvVarName(subSys, Default, param)
		candidates.Remove(paramEnvName)
	}

	isSingleTarget := SubSystemsSingleTargets.Contains(subSys)
	if isSingleTarget && len(candidates) > 0 {
		return Errorf("The following environment variables are unknown: %s",
			strings.Join(candidates.ToSlice(), ", "))
	}