I would be happy if you could read this when you have time.
It would be great if you could read this when you have a chance.
どちらも「お時間のある時に読んでもらえたら嬉しいです。」という意味です。
1) I would be happy if you could read this when you have time.
2) It would be great if you could read this when you have a chance.
「もし〜なら嬉しいです」は
I would be happy if ~
It would be great if ~
と表現できます。
「お時間がある時に」は
when you have time
when you have a chance
と言います。
ご参考になれば幸いです！
日本 
