An expression used to remark that time has passed quickly or to introduce a statement like “it's already...”.
早いもので、もう結婚してから五年になる。
How time flies — it's already been five years since we got married.
早いもので入社してから一年が過ぎた。
Time flies; it's been a year since I joined the company.
早いもので、子どもがもう小学生になった。
Time really flies — my child is already in elementary school.
早いもので、気がつけば夏が終わっていた。
Before I knew it, summer was already over.