וְשָׁמַרְתָּ֛ אֶת־הַחֻקָּ֥ה הַזֹּ֖את לְמוֹעֲדָ֑הּ מִיָּמִ֖ים יָמִֽימָה׃ (ס)
Thou shalt therefore keep this ordinance in its season from year to year.
Rashi on Exodus
מימים ימימה means FROM YEAR TO YEAR (ימים frequently signifies a year) (Menachot 36b).