Getting the time during a transaction

Hi, I am continuing to through a postgres to sqlite conversion and have 
run into this sort of thing.

select tid, extract(epoch from current_timestamp) ...

extract(epoch from current_timestamp) is postgres functionality but is 
there a way to obtain the current_timestamp or similar from sqlite 
(where I can then obtain epoch with my program logic instead)? I need to 
use this for time comparisons but without storing it. Many thanks.

Regards,
David