Apart from Chol HaMoed, are there any other dates that it is not recommended to arrange a matzeivah?
To do the actual erecting and say tehillim at that time is not a problem, except that there are numerous days when we don’t say hespeidim (eulogies). If it is done on those days it will have to be without any hespedim. the days that hespedim are not said are the following: Rosh Chodesh, Chanukah, Tu B’shevat, Purim and Shushan Purim even in a leap year, the entire month of Nissan, Lag B’omer, Isru Chag, From Erev Yom Kippur until after Isru Chag, Erev Shabbos and Rosh Chodesh after Chatzos)
Gesger Hachayim 13, Divrei Torah 5-98, Maharsham 2- Introduction, Tziunei Halacha pg. 613, NIshmas Yisroel 2 pg. 862, Halachos Of Aveilus pg. 339.