Support for conversion of intervals and timestamps to other formats is still not properly supported in Oracle 10g. The problems with the "interval" and "timestamp" data types have been around since version 9i and they haven't been fixed in 10g R2. You just have to ask why? There doesn't even appear to be a work-around by using the cast statement!
Take a look at this little scenario from Andrew Piskorski it shows some examples of how bad the problem is. The advice has to be stick clear of these data types.
