So in fact it does not under record the time, but the distances, hence the slower pace. You can improve the distance under reporting by enabling the "every second recording" mode instead of the default "smart recording" in the System Settings of Instinct, and by enabling the option GPS+Gallileo in the settings of the Run Activity profile. Both options will slightly increase the battery drain.
What could help, is calibrating properly your stride length, for the stride you have during running - the distance shortening happens when Instinct drops the GPS signal for a while. For the section when it is without the signal, it continues measuring the distance, using the stride length, and counting your steps. So, if the stride lenght is set too short, this alternative (non-GPS measured) distance will be shorter than it needs to be.
It is also possible that Instinct somehow adjusts the stride lenght automatically, and in fact it indeed could do it rather easily, but until now I did not verify it experimentally. However if it does, it does not work as it should, since we would not notice the GPS gaps in such case.
garmin instinct is just an inaccurate watch. I tried everything (all permutations of settings, long gps soak, ....) and reached out to support as well but I still get a distance discrepancy of >5% as soon as gps conditions get a bit challenging like some tree cover in a park. I have given up on the instinct for my running training. My 5 year old polar m430 is waaaay more consistent and accurate on my everyday runs. I still use the instinct for hiking though, as there the pace (and distance) don't matter so much. Still I wish I didn't bought the instinct.
