Finally, you need to adjust the formula for the GMT offset. For example, if you're in New York the GMT offset is -5. Therefore, the final formula is:
=(((B2/60)/60)/24)+DATE(1970,1,1)+(+8/24)
E.g.
| values:Timestamp | GMT8 |
| 1433727278 | 6/8/15 9:34 |
| 1433727545 | 6/8/15 9:39 |