While there is not 100% right or wrong answer to this question, a good rule of thumb is 1 to max. 2 minutes.
To give you a bit more orientation concerning appropriate timing, the following 3 aspects need to be in line:
- Time which you take to prepare your structure
- Complexity of the case outline
- Depth and precision of your prepared structure
So if the case outline is very simple and you come up with a rather shallow generic structure, 2 minutes is definitely way too much. On the contrary, if the case outline is rather complex and you present a super-mece in-depth approach for that case, 1:45 is very fast - and your interviewers know that.
After 2 minutes the interviewer will most likely interrupt you (chances increasing exponentially each second afterwards) and force you to present the structure which you have at that point in time. For practice, rather try to be closer to the 1 minute mark - it forces your brain to process this part of the case very quickly (although quality is more imporant obviously), and at the end of the day it's mostly just practice and not rocket science.
Hope that helps - if so, please be so kind to give it a thumbs-up with the green upvote button below!