They were born four hours after I arrived at the hospital.
"病院についてから4時間で産まれた"
- They were born four hours after I arrived at the hospital.
- She/he was born four hours after I got to the hospital.
- The baby was born in four hours after arriving at the hospital.
I got to the hospital at nine o'clock at night and my baby was born four hours later.
この場合、次のような言い方ができますよ。
ーI got to the hospital at nine o'clock at night and my baby was born four hours later.
「夜の9時に病院に着き、4時間後に赤ちゃんが産まれた」
to get to the hospital で「病院に着く」
ご参考まで！
アメリカ合衆国 
カナダ 
