My idea would be to tune the instrument when the room is at 25c. My rough calculations are that flue pipes sharpen by approx 0.6 Hz per degree Celsius. Therefore if the temperature at the beginning of the concert is say, 22c, your reed rank is going to be sharp by almost 2 Hz. Hopefully, by the end of the concert and the temperature perhaps as high as 27c, the reeds will be still no more than 2 Hz different from the flues. The overall pitch of the instrument has no consequence unless other instruments are involved.
This is a very rough guide and does not take into consideration the temperature at different levels in the room.