Date and time will be your server (you won't know their time).
IP can be spoofed, so that is not very accurate.
GPS can be close, or not close ... depends on where they are and who their ISP is.
You won't know their ISP ... they could be using WiFi from anywhere.
I would say the only thing you might know for sure is the date.
Google analytics would be the best way to get as accurate as possible.
But, they are sort of guessing too.