Client currently has a large SIMPLE IRA and this is the only tax-deferred IRA assets client he has.  He also has an existing Roth IRA and a 401k with his employer (self-employed).   He would like to make a back-door Roth IRA contribution which is of course poses an issue because of the SIMPLE IRA.

They are considering rolling the balance of that SIMPLE into his 401k this week (assuming that it has been held for 2 years).

Here’s the timeline question:   If he waits until after the SIMPLE is moved into the 401k can he immediately begin to do the back-door Roth (i.e., open a new traditional IRA, make a non-deductible contribution, immediately convert it over to his Roth?)  OR does he have to wait until the next tax year?   We are unsure if the IRS sees that he has tax-deferred IRA assets in the same year that he does the backdoor Roth conversion if they will still consider the Simple assets for pro rata purposes (even though they are going to be rolled into 401k).  In short, is there a timeline/lookback period for something like this?

Thank you for any information you have on this topic!