Sorry to take time off, especially during this busy season.
I feel really bad about missing work during one of the busiest times of the year.
この場合、次のような言い方ができますよ。
ーSorry to take time off, especially during this busy season.
「特にこの忙しい時期に休みを取ってすみません」
to take time off で「休みを取る」
ーI feel really bad about missing work during one of the busiest times of the year.
「1年で一番忙しい時期の1つに、仕事を休んで申し訳ないです」
to miss work で「仕事を休む」
ご参考まで！
カナダ 
