poppa-bar-abba:- You should make Aliya immediately without any delay, so that you shall only have to keep 1 day Yom Tov this Shovu’os, and you would be able to fulfill 8 Mitzvos Asseh d’Orraisso vis a vis Tefillin this Thursday.
Even if you only decde during the middle of this Thursday when in Israel that you are making Aliya, you immediately discontinue Yom Tov Sheni and make Havdolo and lay Tefillin on that very day.