The 5-year beginning date for qualification of the Roth 457(b) account does not transfer to the Roth IRA when the Roth 457(b) account is rolled over to the Roth IRA. The beginning of the 5-year qualification period for your Roth IRAs begins on January 1 of the year for which your first contribution to the Roth IRA is made. If the rollover establishes your first Roth IRA, the 5-year Roth IRA qualification period will start on January 1 of the year in which the deposit is made to the Roth IRA.
Any 5-year holding period for In-plan Roth Rollovers in the 457(b) does carry over to the Roth IRA as a conversion holding period when rolled over.
If the distribution from the Roth 457(b) would be a qualified distribution (both the 5-year and age 59½ requirements have been met) if not rolled over, the entire amount rolled over to the Roth IRA becomes contribution basis in the Roth IRA, otherwise only the contribution basis from the Roth 457(b) becomes contribution basis in the Roth IRA.
