The deadline to complete the rollover is October 15, 2024, but only if your file your tax return or request a filing extension by April 15. If you intend to roll the distribution over by the deadline, it would probably be best to request a filing extension by April 15, pay any balance that would be due under the assumption that you will complete the rollover by October 15, then, if you don't complete the rollover, file the tax return reporting whatever amount you do end up rolling over and pay any additional amount due. If you pay with your request for filing extension 90% of your eventual tax liability, you'll get an automatic waiver of any penalty or interest on the additional tax that needs to be paid with your filing.
