Hi,
This is the SQL query used in postgres:

select distinct tag_serialno from process_instances where tag_serialno='"+tag_serialno[i] +"' and state_id='"+ prevStateid +"' and timestamp_mi('" + dt + "',start_date) <= '" + timeperiod + "';");

in the above query timestamp_mi function is used to get the timestamp difference between the current time and the time specified in the start_date column.

Is there any built in function in hibernate to get this difference calculation.
Can someone please help me out?????

HQL isn't like SQL like that. Just get the two Date objects, call getTime() and do the comparison yourself in Java...