It doesn’t give current time. It gives the number of milliseconds that have passed since January 1, 1970 (UTC)
timestamp won’t limit it to 24 hours. I’m guessing you’ve read my response in this post and misunderstood it.
To get the number of hours, divide the difference between 2 timestamps by 3,600,000.
To get the number of days, divide the difference between 2 timestamps by 86,400,000 (or divide the number of hours by 24).