You need to uncheck the box next to "Delay disconnection by provider to the period between"
That will stop you from being disconnected.
Sadly, that doesn't always work. I have been using F!Bs now for many years (7390/7490 and now 7590). A lot of the Beta software re-introduces the daily disconnection irrespective of the user setting. I have just upgraded my 7590 to Fritz!OS 7 and there is no daily disconnect.
The 'good news' is that the disconnection will not result in a hard connection break; ie, it doesn't result in DSL re-training. It follows the speeds that you have prior to and after the 'break' will be the same.