When should we do Sehaj path?

Can we do Sehaj path on phone?
YES you can. There is no harm as long as your mind is focused and your intentions are pure. If you read from Guru Granth Sahib Ji and your mind is wandering somewhere else then there's no point of doing such Path. And if you are doing on phone and learning or gaining something.
How long is Sehaj path?
Sehaj Sahib Paath (or Sadharan Paath) – is the reading of the entire Sri Guru Granth Sahib. This is usually accomplished with in six to seven days in discussion with the family arranging the Sehaj Sahib Paath.
Where is the real Guru Granth Sahib kept?
The original Guru Granth Sahib is in the possession of the Sodhi family of Kartarpur village, and is placed at Gurdwara Thum Sahib. The Sodhis are descendants of Guru Arjan Dev and Kartarpur was founded by him in 1598. Since the early 20th century, it has been printed in a standard edition of 1430 Angs.

