Problem: The email notification after an enrollment should be sent to an other email-address (not to site administrators in REM). Is it possible hook up on REM's notification-procedure in order to...

These changes are done for each site collection.
You can do it using PowerShell script:

$site = GET-SPSite -identity http://your_organizatioin_url
$site.RootWeb.RegionalSettings.WorkDayStartHour =480
$site.RootWeb.RegionalSettings.WorkDayEndHour =960
$site.RootWeb.Update();


The possible values you can set for WorkDayStartHour and WorkDayEndHour are 60 x (hour value in 24 hour format).

Basically, they are total number of minutes. For example,

6am = 6 x 60 = 360

6pm = 18 x 60 = 1080

9pm = 21 x 60 = 1260 and so on..

For reference see Time formatting in the article http://www.jamestsai.net/Blog/post/How-to-change-SharePoint-Calendar-default-start-hour-and-end-hour-of-Day-View.aspx