cron_last vs node_cron_last variable I wanted to get the time of last node update (any node). So, then I thought I could simple pick last cron run time ( because I am using feeds module to pull the RSS feeds so nodes will be updated on every cron run ). but then I discovered another variable "node_cron_last".

Can anyone explain me the difference between two variables, what value they contain?
The only place node_cron_last is set is in _node_index_node(), which is run when indexing a node for search results.
Its purpose, per the comments:

Save the changed time of the most recent indexed node, for the search results half-life calculation.

cron_last is simply used to

Record cron time.

per drupal_cron_run()
Given that REQUEST_TIME is used for all values (cron variables + node changed date) in the same request, you might well expect those two variables to contain the same value.