This year since Yom Hazikaron begins on Motzaei Shabbat (4 Iyar), the Government has pushed its observance to Sunday night (5 Iyar) to avoid Chillul Shabbat. Yom Haatzmaut will be celebrated beginning on Monday night (6 Iyar). When should Hallel (and the rest of the Tefillah Hagigit) be recited, and is there any difference for those in Galut (I understand that when 5 Iyar falls on Motzaei Shabbat and is thus celebrated the preceding Thursday - there is a dispute when to celebrate in the Galut since the chance of Chilul Shabbat is less since we do have have parades, etc...)? Also, if in Galut Yom Hazikkaron is not commemorate on Motzaei Shabbat, would it be permissible to have a Chanukat Habayit on that Motzaei Shabbat?
The date celebrated world-wide is the one determined by the State of Israel in consultation with the Israeli Chief Rabbinate.