It is important to note that changing the time format in the Regional and Language Options in the control panel does not change it for the Local System account, which in case is the account that Lotus Domino runs under when configured to run as a service. Unfortunately there is no special Control Panel to change the settings for the Local Systems account in Windows.

There are to possible options to overcome this issue. First and foremost a special user could be created that is solely used to authenticate the Domino service against the system. This is certainly the preferred option for a professional Windows systems administrator.

Alternatively the setting can be changed tweaking the user settings in the HKEY_USERS\ .Default registry hive. In Windows 2003 the keys in question where s1159 (a.m.) and s2359 (p.m.). Both keys are found at HKEY_USERS\ .Default\Control Panel\International.

Please note that as with all changes to the Windows registry special care should be taken and I would like to take the same approach as all other vendors telling that no changes to the registry should be made without consulting the Microsoft support first and all changes are made at your own risk.