More info needed
You state that you lost 5 minutes and no difference in fuel.
How did you compare the outcome of the 2 situations? Are you talking about the FMC arrival estimates before and after the climb or are you comparing the actual arrival after flying at FL390 with the forecast figures that you had noted at FL330?
If you talk about both estimates, were the wind figures for the whole route FL390 inserted? If not, an estimate for a long flight to destination could be somewhat in error.
If you talk about the actual figures after arriving at destination, the difference could be in extensive approach vectoring, and the result from staying at FL330 could have been even worse.
And of course, as BOAC noted, if the remaining flight time was short, you may not have gained back the fuel used for the climb from FL330 to FL390.