Question

Can an unveiling be conducted during Passover? Is there any other time in the year when an unveiling cannot take place aside from the Shabbath?

Answer

There are no specific laws or requirements concerning the unveiling. In fact, it is a relatively new custom to perform unveilings. In Europe and Russia, before WW II, the monuments were erected by the sexton of the synagogue, and even the family did not attend - (source: "Igrot Moshe" by R' M. Feinstein, Y.D. IV 61).

Therefore, except for Shabbat and Jewish holidays: Rosh HaShana, Yom Kippur, Succot, Chanuka, Purim, Passover and Shavuot; you should not schedule an unveiling. The reason being that they are days of rejoicing.

Thus, unveilings are customarily not scheduled throughout Passover including Chol HaMoed (the intermediate days).