Set to install auto updates within a specified time period

Default policy is "0000-0400". This policy depends on AU2_InstallAtIdleTime, if AU2_InstallAtIdleTime is disabled, AU2_SafeUpgradePeriod will not work. If this policy is empty or invalid, client will install auto updates within the default time period when idle. If this policy is a valid string, client will install auto updates within the specified time period when idle. The format of this string should be HHMM-HHMM, for example: "0900-1800" means 09:00 to 18:00, "1800-0400" means 18:00 to the next day 04:00. If this setting is not set, client will use the default setting.