And as to why the correct time might actually be important, in the absence of radar, or other accurate means of position fixing that are usable by ATC, the required separation standard is calculated using those block times between reporting points. Introduce a couple of apparently minor inaccuracies..just a minute or two at each end, say, and someone else does the same thing, you could possibly end up with half the required space between 2 a/c at the same level.