It's a result of the computer's programming.
In many modern computers (Linux, macOS, iOS, Android, basically everything except Windows), computers keep track of the time by counting the number of seconds since January 1, 1970 (because this scheme was created in the early 70's). This is called Unix time.
Somewhere in your time machine's code, the time is limited to -895,852,800. Maybe that was the programmer's phone number. Maybe they were lottery-winning numbers. Most realistically, if you're flexible with the date, they rounded it off to -900,000,000 (June 25, 1941). (Unfortunately, there's no powers of 2 that are sufficiently close.)