In Bulgaria "Ivet" does not have a nameday on 7th January. In Bulgaria "Ivet" does not have a nameday. One of the 2 Iva's namedays is on 7th January (the day of St John the Baptist according to the Orthodox Calender).
In Bulgaria "Iveta" is the commonly used cognate of Yvette. To be perfectly honest Ivet doesn't sound Bulgarian at all and is rarely used. The bearers of the name usually celebrate their name days on 7 January (St. John's Day).