Time difference between consecutive points QGIS

Question

I have a shapefile with a timestamp (string type) and id field (string type):

timestamp             tag  id
2017-11-14 09:03:00    1    0
2017-11-14 13:03:00    1    1
2017-11-14 20:03:00    1    2
2017-11-14 09:03:00    2    3
2017-11-14 13:03:00    2    4

I'm trying to find the time difference in hours between consecutive points by id using the Field Calculator tool in QGIS.

I tried the following expression but the results returned NULL. When I try to convert the timestamp field to DateTime using to_datetime function I get an error that it can not convert to DateTime. Any other suggestions on calculating the time difference with the Field Calculator in QGIS?

 second(age(attribute($currentfeature, to_datetime(timestamp)), 
           attribute(get_feature_by_id('points',$id-1), to_datetime(timestamp))))

Answer 1

This will do it:

hour(age(
 to_datetime(attribute($currentfeature,'timestamp')),
 to_datetime(attribute(get_feature_by_id('points',$id-1),'timestamp'))
))

Results are in hours as specified.
In my case, I used this to populate a column "timedif":

---

Difference in seconds would be:

second(age(
 to_datetime(attribute($currentfeature,'timestamp')),
 to_datetime(attribute(get_feature_by_id('points',$id-1),'timestamp'))
))