The double click interval time setting in KDE is just ignored. Furthermore the triple click interval is extremely long, strangely longer than the double click interval, which is annoying when you try to double click and drag. I imagine this has something to do with libinput not being properly supported. So how do you change the triple click interval in libinput?
Yes, it does seem to me that the Plasma 5 ‘Input Devices’ config utility is work-in-progress with respect to lbinput. All that is available to configure is outlined in ‘man libinput’, so that should be your starting point.
Just to clarify, do you mean ‘three finger tap’ as described here?
No, I mean clicking 3 times to highlight the whole paragraph.
It’s not something I consciously tend to do, although testing this just now works for me with three fast taps (or left-clicks). If it’s not working as expected for you I can only suggest submitting a bug report perhaps.
The problem is that the interval is too long, so when I try to double click, and then drag the selected word, I often end up triple clicking instead.
It’s a balancing act I guess.
The behaviour explained here
http://who-t.blogspot.co.nz/2015/06/extended-tap-and-drag-in-libinput.html