Group field disabled

LUTissue.PNG

Hello,

I am starting with look-up table and I am facing what seems to be a recurrent issue:

I have in a column of my LUT hours and I would like to group those hours.
Note that I've already browsed forums (the format of the data is hours both in sources and in the pivot table, there is no blank within the data).

Thanks if you have any idea on what could be the error.

OK I found the issue..
Even when changing the cell format of my data to hours, it wasn't effective : Data was still considered as text.
To change it I had to select the column and click on Text-to-Column. Then I was able to group my data per hour.

I hope this could help someone in the future.