Change duration in the agenda Meetings

Is your feature request related to a problem? Please describe.
Admins can add an agenda of the meetings so that the users could see how the meeting will take place. When creating the agenda, the duration of each slot should be in minutes then the start and the end hour are automatically calculated (which will be displayed on the front office).

The problem here is that if there is any break between two slots, the admin should add it to the agenda or the calculs will be wrong. It is particularly true when the meeting lasts for multiple days. 

Describe the solution you'd like
We'd like to give the admin the possibility to set the start and the end hour of each slot in his/her meeting. We suggest to add a calendar field instead of the duration in minutes. 

Additional context

Does this issue could impact on users private data?
No

Funded by

Could be funded by Open Source Politics.