Board Thread:Questions and Answers/@comment-27682957-20160126215523/@comment-32029088-20170517205125

There's not really way of knowing when she actually first appeared in 1967 since the Silver Age was incredibly convoluted and didn't have much of a timeline.

In Post Crisis continuity: According to Batman: Year Three and Batman: Dark Victory, Dick first became Robin in Batman's third year on the job. I assume Dick was Robin for at least one or two years before Barbara emerged, so like you said around his fourth year as Batman.