You can change the units with the desktop version, in the settings ou by clicking on the unit scale on the right corner, bottom.
Once done, the changes will be saved and visible on all other devices so phone, tablet,...
If you look your data for Saturday the 13th of August, you see 0.4mm at 5.00AM. This is the total of rain accumulation between 2.00AM and 5.00AM. Then you see 0.9mm at 8.00AM. This is the total of rain between 5.00AM and 8.00AM.
If you go for Windy Premium, by splitting from 3h forecast to 1h forecast, you will see how the rain fall is spread by 1h in place of seeing the accumulation over 3h : for instance, you could have 0.2mm at 4.00AM and 0.2mm at 5.00AM as a potential example