Even though I didn't eat my bento right away, it was still really good.
I didn't eat my bento for a few hours after I bought it, but it was still delicious when I finally ate it.
この場合、次のように言うと良いでしょう。
ーEven though I didn't eat my bento right away, it was still really good.
「すぐに弁当を食べなかったけど、まだとても美味しかった」
right away で「すぐに」
ーI didn't eat my bento for a few hours after I bought it, but it was still delicious when I finally ate it.
「買った後数時間、弁当を食べなかったけど、やっと食べた時まだ美味しかった」
for a few hours after ... で「…後数時間」
when I finally ... で「やっと…した時」
ご参考まで！
カナダ 
