@grishka so you're going against default conventions both in JVM (new Date(ms) and date.getTime()) and in JS (new Date(ms) and date.valueOf())? (possibly somewhere else, idk)
What I'm saying is, if picking a number-based timestamp format, I'd pick unixtime in milliseconds. I thing it would be the least surprising option.
iliazeus, at least PHP's time() returns unixtime in seconds so there are examples of both.