For example, time passing for one day of Brahma is not the same as time passing for one day of Pitrs is not the same as time passing for one day of Humans, etc,.
Different lokas reside on different astral planes thus what I think is that they must be having their own star/stars like our Sun. Thus their time relatively differs from ours.
Just want to mention some interesting things that I have read about lokas in the book Muktananda Wagishwari by saint Muktananda.
- Pitruloka's one day is equivalent to an year of earth. Thus we do Tarpan Vidhi or Shraadh every year in Pitru Paksha.
2.There is Sidhaloka where all saints and sages live.
3.Hell is a truth and not a myth. Hell has rather Raurav Narak has rocks of faecal matter and urine etc.
4.There are many other lokas like Shastras say like Chandraloka, Suryaloka, Satyaloka and shastras are very true.
Astral planes are very different and our human body can not be used to go there, only our astral body can travel various lokas.
Thats all I know.. hope it helped...