Never. Their platforms may have changed some over the years, but the switch wasn't as radical as liberals like to pretend it was. That's just an excuse they make to keep repeating the lie that the racist Democrats joined the GOP after Johnson signed the Civil Rights Act.
That's not a lie at all. The Civil Rights Act of 1964 set in motion the South's turn from D to R, hence why Barry Goldwater won 4 states that would have been easily for Johnson in any other circumstance. They fell in love with Reagan and the GOP in 1980 because of his dog whistle racism, and have voted Republican ever since. Since 1976, the Republicans have run further and further to the right, embracing racism more and more with each passing election.