Aggregate functions on DATE and TIME

As far as I can see, the aggregate functon MAX isn't defined for type
TIME. I desperately need to extract the last sample for each day from
a database, and tried this statement:

SELECT MAX(time),date FROM samples GROUP BY date;

where the table samples contains

date DATE,
time TIME,

I get the following error:

ERROR: function max(time) does not exist

I've tried casting the time to a type for which MAX is defined, but I
was unable to find a casting function that was valid.

My questions are: Why isn't MAX defined for TIME? Will it be defined
in the future (no news about it in the 6.4-BETA1 HISTORY-file)? Any
alternative ways to get the result I want?

Thanks for your time!

Sverre.

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