The best of all possible times to have a leap second
Is midnight UTC on 31st December
If only because here in Enn Zedd it's lunchtime on New Year's Day and there's hardly any work being done so if things do go TITSUP, mostly nobody will notice. On account of being on summer holiday and only being concerned about cold beer and hot BBQs - neither of which will mind too much if there's an NTP hiccup
The last time they changed it on 30th June which was potentially a real PITA as lunchtime (NZ) 1st July is just an ordinary busy work time.