It's the third anniversary and there's no tombstone yet. Can we wait until the third anniversary?

Of course. According to some traditional customs, the time to erect a monument for the deceased relatives is after the third anniversary, or in Tomb-Sweeping Day, the first day of October and other major sacrificial festivals. In the specific time selection, we should also choose the auspicious day of the ecliptic to avoid a direct conflict with the deceased who set up the monument and avoid bringing disadvantages to their loved ones. Therefore, if the monument is erected before the third anniversary, it can be announced until the third anniversary.