Merriam-Webster Collegiate Dictionary - early on

 adverb  Date: 1928 at or during an early point or stage the reasons were obvious ~ in the experiment Usage:  This adverb is sometimes objected to in American writing as an obtrusive Briticism. It is a relative newcomer to the language, having arisen in British English around 1928. It seems to have filled a need, however. It came into frequent use in American English in the late 1960s and is now well established on both sides of the Atlantic in both speech and writing.