Martijn,

> No, this isn't a "time", it's a "duration" or "interval". Something

which

> Firebird doesn't support.
>

Firebird supports mathmatic, it is enough.

> Format it at the client side or write a Stored Procedure for it.

you can format it everywhere with cast
cast(myhours||':'||myminutes||':'||myseconds as time)

As i said some months ago here...
Time is time, it is a special, counter display system.
can i ask how many times will i explain the time.
i m asking with how many "times".
because of time is a repeat counter.
You live in holland in time of 20:15:00
But i am in Turkey in time 21:15:09
as you see, we are living in the same time(!) but in the different
counter location.
time is logical/virtual/mathmatical/locational term.
we are using a geographical tuned time version.
as a human, we cant count, interpret too much numbers.
so we are using a special format 60 based numbering system.
00:00:00 = first second of counter
23:59:59 = 3600. second of counter

geographical time(time zone) says how many atomic radiation frequence
wave passed since first meridian.

you can play with time every time.(daylight savings for example)
there is no statical cosmic time or point.

Time is a special numbering system based on 60.
we are using 10 based numbering system as human.
So, time is also a interval or duration, but in a special format.
we can convert a time to a ten based numbering with:
mytime-cast('00:00' as time)= myinterval
and we can vice versa with:
cast('00:00' as time)+myinterval = mytime
There is no magic or holy, time is a numeric format like integer or
float.

Regards.
Ali