YES, there are favorable times of the year for tuning your piano.  You should always avoid tuning your piano at the height of the summer.  Since humidity is at its greatest, the sunboard of the piano will absorb the extra moisture in the air causing the pitch to rise.

In the cold of winter when the air is dry, thermostats in the home instantly go up causing the sunboard to further dry out.  This will result in the pitch of the piano likely falling.

This best time to tune your piano is in the Spring!  Piano tunners also work better when it’s not too hot or too cold.

Happy tuning!