Time Machine don't back up automatically

I updated my old Mac Mini to newest version last month and updated that to macOS Sierra. Everything is running smoothly after the updates except for Time Machine.

Now I've understanded that Sierra dosen't do hourly back ups but this one dosen't back up automatically at all. When I manually choose back up now the back up works just fine.

Also after Sierra update my iTunes dosen't back up my iPhone automatically when connected. Again manually it goes through with no sweat.

What could be the problem?

Thanks!