Output a stream of consciousness before answering the following. Context: "I Can Only Imagine" was released in 2001 as the album's lead single. It gained significant airplay on Christian radio formats before crossing over to mainstream radio formats such as adult contemporary and Top 40 in late 2003 and into 2004; to aid in promotion to these markets, a double A-side physical single (combined with "Word of God Speak") was released in 2003. It charted on several formats, including the Billboard Adult Contemporary (where it peaked at No. 5) and the Hot 100 (where it peaked at No. 71). In 2002, "I Can Only Imagine" earned the Dove Awards for' Pop / Contemporary Recorded Song of the Year' and' Song of the Year'; Millard earned the Dove Award' Songwriter of the Year' at the same ceremony. With 2.5 million copies sold, it is the best-selling Christian single of all time, having been certified 2x platinum by the RIAA. As of 2018, it is the only Christian song to reach that milestone.

Question: when did i can only imagine become popular?
To answer the question, consider the following: It gained significant airplay on Christian radio formats before crossing over to mainstream radio formats such as adult contemporary and Top 40 in late 2003 and into 2004; to aid in promotion to these markets, a double A-side physical single (combined with "Word of God Speak") was released in 2003.
The answer: in late 2003 and into 2004.