Interesting that they provide last login dates as Unix milliseconds, but rounded to day boundaries (each of these is at midnight UTC). I'd assume that's what they store, which is good, but it's odd that they provide the data with such unnecessary precision if so.

I wondered originally if this would help disambiguate accounts, perhaps if two numbers last logged in at the same timestamp one could guess that they were on the same device or something, but this doesn't look possible.