Sorry. It was my mistake. I used this number '0.0000115740695036948' which is for 1 second like time + (randbetween(5,7) * this number). I generated the date time manually like this to test the formula. Now I realise that if I work on the imported data (or just TIME function) I would have got the correct result.
Thank you for your assistance and apologize for misdirecting you.