var log_time ="15/7/2017 9:30:46" .split(" ");

log_time[0]=log_time[0].split("/").reverse().map((el,i)=>i?("0"+el).slice(-2):el).join("-");//5/4/2017 => 2017-05-04

​

log_time[1]=("0"+log_time[1]).slice(-8);

​

console.log(log_time);

​

var difference= new Date() - new Date(log_time.join("T"));

var hours=Math.floor(difference/(1000*60*60 /* one hour in ms */));

​

console.log(hours);