STEP 1-- CREATE ITEM "P115_START_TIME" AS SELECT LIST
QUERY--

select to_char(TO_DATE('01/01/2021 09:00:00','DD/MM/YYYY HH:MI:SS') + (1/1440*(level-1)*15),'HH:MI AM') DISPLAY ,
to_char(TO_DATE('01/01/2021 09:00:00','DD/MM/YYYY HH:MI:SS') + (1/1440*(level-1)*15),'DD/MM/YYYY HH:MI AM') RETURN_VAL
from dual CONNECT BY LEVEL<97;

NOTE- Format Mask===>DD/MM/YYYY HH:MI AM

STEP 2-- CREATE SECOND ITEM "P115_END_TIME" AS SELECT LIST

QUERY--
select TO_CHAR(TO_DATE(:P115_START_TIME,'DD/MM/YYYY HH:MI AM') + (1/1440*(level-1)*15),'HH:MI AM')||
CASE WHEN (((level-1)*15))/60 >1 THEN
CASE WHEN MOD(((level-1)*15),60)> 0 THEN '( '|| FLOOR((((level-1)*15))/60)||' HOURS '|| MOD(((level-1)*15),60)||' MINUTES )'
ELSE '( '||(((level-1)*15))/60||' HOURS)'
END
ELSE
CASE WHEN ((level-1)*15)=0 THEN '( 0 MINUTES )'
ELSE
CASE WHEN MOD(((level-1)*15),60) = 0 THEN '( 1 HOURS )'
ELSE '( '||MOD(((level-1)*15),60)||' MINUTES )'
END
END
END AS DD ,
((level-1)*15) RR //--RETURN VALUE AS YOUR REQUIREMENT

from dual CONNECT BY LEVEL<97

Cascading List of Values --
PARENT ITEM-- P115_START_TIME