Formally, Hannah has to agree on your Urlaub (and she anyway has to sign your Urlaubskarte). But in most cases, you don't have to ask her explicitly when you want to take Urlaub. If none of the items in the following checklist is problematic, you can assume that she agrees. If there is a major update of this checklist, you will be informed by mail. So you don't have to go to this page every time to check that nothing has changed.
1. Make sure you enter your Urlaub in the AD calendar
2. Check that your Urlaub does not conflict with any teaching duties (like tutoring or assisting a course). If you can't avoid it or you feel that your Urlaub at that particular time is more important, you should take care of an adequate substitute.
3. Check that your Urlaub does not conflict with the correction of exams (important special case of 1). Our exams are usually in the first weeks after the end of the semester and they are entered into the AD calendar as soon as we know the date.
4. Check that your Urlaub does not conflict with any important deadlines (e.g., a submission deadline).
5. When you are in doubt, you can of course always ask Hannah.
6. When you want to take Urlaub for an unusually long time at a stretch (a month or more), better do ask some time in advance.