Calculate time duration of status of ticket

I have a table which keeps track of status change of ticket.

I would like to get the duration of each status for each ticket. I have tried something like below.

select t1.ticketID,t1.new_value,TRUNC( t2.changeddate ) - TRUNC( t1.changeddate )  
duration 
from ticket_table t1 
join ticket_table t2 on t1.ticketid = t2.ticketid 
and t2.changeddate < t1.changeddate 
group by t1.ticketid,t1.t1.new_value
order by t1.ticketid,t1.new_value

Even if you don't tell it in the question, I think what you noticed is that joining on t2.changeddate < t1.changeddate will compare each status with all its predecessors.

To restrict the side-by-side comparison of statuses to only 1 row, you'd want to look for the lead() window function that will give each row access to its immediate successor's columns:

select t.*, lead(changeddate) over (partition by ticketID order by changeddate) - t.changeddate duration
from ticket_table t
order by t.ticketid,t.changeddate;

(as output in the demo fiddle)