Q. Since one is not allowed to prepare from Shabbat to Yom Tov, can one sleep on this year’s Shabbat Erev Shavuot afternoon more than usual, if he has the intention of being able to learn Torah during Shavuot night?
A. Mishna Berura (290: 4) quoting Magen Avraham and Sefer Chasidim rules that one should not say, let’s sleep so we will be able to to work Motzei Shabbos.
Shaarei Halochos on Hilchos Sefiras Haomer (11: 2: n. 2) presents different opinions as to the prohibition involved. It could be hachono or preparing from Shabbos to Yom Tov, but it would be permitted if his main intention is for resting on Shabbos. It could be also included in the Vedabru Dobor proscription or expressing intentions that one is going to do a melocho after Shabbos.
Either way, Horav Shmuel Kamenetzki Shlit’a (ibid.) rules that it is permitted, but one should not say that he is resting on Shabbos so he will be able to stay up at night, even if it is a great mitzva to do so.
Sho’ne Halochos (quoted in Zechiras Shabbos Ushmirosso 15: 3) also permits and compares it to eating more than usual on Shabbos Erev Tisha Beav. Similarly he rules, that the intention is permitted, but not the expression.
Horav Shlomo Miller’s Shlit’a opinion is similar.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit’a