GE just looks for the earliest and latest entries and uses the resulting interval. I'm not sure I understand exactly what you mean by limitations. Eg: if you have only two kills a day apart the slider will be 2 days long.
As for career wide statistics you need to concatenate more patrol reports. Like export the patrol log before ending the patrol (aka before the data moves to careertrack.upc, date-time stamps get messed up and coordinates are encoded with Enigma
) for each patrol.
Should I add an option to select multiple KMLs and build a big one out of them with all the kills?