Thanks for an easy question, for a change!
Traditionally, there is no Jewish ceremony of an “unveiling”. There is a ceremony called “Hakamat Matzayvah”
ä÷îú îöáä, or “Erection of a Tombstone”. There are differing practices as to when this is done. Some do so right after shiva, many after shloshim (30 days), some on the first yahrzeit (anniversary of the death), or a convenient date near that time. This topic was discussed on JVO
here.
As to the cheesecloth, I wish to quote directly from the Rabbis manual of the Rabbinical Council of America:
The important matter is to erect the memorial. The timing of any gathering to recite prayers at the site is not as pressing an issue.
Also it is important to know that this gathering is not an unveiling, and the placing of a sheet on the monument to be unveiled, is pure nonsense.
I could not agree more. The usage of a “veil” is a Christian custom, and there is no good reason to make it part of Jewish practice, and plenty of reasons to avoid it, as it is prohibited by Halacha to adopt non-Jewish religious practices as our own.