I kbow that this is an older post, but I am hoping that I can put some light where there seems to be very little.
First, if you can, change that timer for the deletion of files.
If you continue doing what you have in the past, it should not need to be active in the first place.
Second, a folder/file called .thumbnails or the like is what is often referred to as a 'junk' file. Thumbnails are the low resolution, tiny pictures that you see when looking through thepics and videos on your device.
These thumbnails greatly speed up the loading time of the menu in apps like Gallery and Video Player.
Generally, lower quality apps like the ones that come with a device use these, and each app can want an entire set of them for each piece of media.
On a lower end device (like mine), this can quickly consume an undesireable amount of memory.
Luckily, I found a Gallery app that is also an editor and a video player- and that does not need thumbnails at all.
Even with thousands of photos and hundreds of videos, the app loads up in mere seconds.
Simple Gallery Pro, by SimpleMobile Tools
Most large app stores have this app.
In my device, thumbnails were stored inside a folder called .thumbnails inside the DCIM folder.
The trick to keep thumbnails from reappearing again and again is to delete the .thumbnail FOLDER and then add a .thumbnail FILE in its place.
This fools the system into thinking that thumbnails exist, so it does not make more.
The period before the folder/file is very important, as this is how the system knows that the media is 'hidden'.
So when attempting this action, be sure to click 'Show Hidden Files' in the File Manager.
There is also a File Manager app made by the same Simple Mobile Tools, called Simple File Manager Pro.
The two work great together.
Also, the Gallery app mentioned above also has a 'recycle bin' that is extra insurance against unwanted deletion of files.
Because the app also allows the viewing of 'hidden' media, you can even look at your thumbnails before deleting them.
