CASE WHEN expression in oracle - sql

Question

I have built a CASE WHEN expression to show me when someone has no system transaction in the system under their user id for anything greater then 15 minutes.
case
when MOD_DATE_TIME > prior MOD_DATE_TIME+(1/96)
and user_id = prior user_id
then round((MOD_DATE_TIME - prior MOD_DATE_TIME)*1440,2)
else null
end as TIME_GAP
That above is the case when statement only. The full query is below:
select
user_id, MENU_OPTN_NAME, MOD_DATE_TIME,
case
when MOD_DATE_TIME > prior MOD_DATE_TIME+(1/96) and user_id = prior user_id then round((MOD_DATE_TIME - prior MOD_DATE_TIME)*1440,2)
else null
end as TIME_GAP
from
(select
ptt.user_id, MENU_OPTN_NAME, ptt.MOD_DATE_TIME,
row_number() over (partition by ptt.user_id order by ptt.MOD_DATE_TIME) seq
from PROD_TRKG_TRAN ptt
join cd_master cm on
ptt.cd_master_id = cm.cd_master_id
Where
MENU_OPTN_NAME = 'Cycle Cnt {Reserve}' --CHANGE BASED ON WHAT YOUR TRACKING... MENU NAMES AT THE BOTTOM
and ptt.user_id = 'LLEE1' --CHANGE BASED ON WHO YOU WANT TO TRACK FOR A GAP...
and cm.cd_master_id =
(select cd_master_id
from cd_master
where
co = '&CO'
and div = '&DIV')
and ptt.create_date_time >=
/*Today*/ trunc(sysdate)
--/*This Week*/ trunc(sysdate-(to_char(sysdate,'D')-1))
--/*This Month*/ trunc(sysdate)-(to_char(sysdate,'DD')-1)
--/*Date Range*/ '&FromDate' and ptt.create_date_time-1 < '&ToDate'
--group by ptt.user_id
)cc
CONNECT BY
user_id = prior user_id
and seq = prior seq+1
start with
seq = 1
What I want the query to do is in the CASE WHEN clause. I want it to account for the shift start time being 4pm, so if they don't do anything till 4:41PM then I would see that listed as a 41 min gap.