ORA-00932: inconsistent datatypes: expected NUMBER got INTERVAL DAY TO SECOND

It looks like you are trying to do maths (+, -) with TIMESTAMP.

If you try to sum or subtract two timestamps, you will get:

ORA-00932: inconsistent datatypes: expected NUMBER got INTERVAL DAY TO SECOND


TIMESTAMP doesn't like that. you should CAST the TIMESTAMP to DATE:

rather than
bla - blu (where bla and blu are TIMESTAMP)
do
CAST (bla as DATE) - CAST (blu as DATE)

and you will get a NUMBER (multiply it by 3600 * 24 and you will turn it into seconds)

BUT
you will lose the millisecond info


Here you have the definition of the TIMESTAMP