Within a tax-exempt account like a traditional or Roth IRA or 401k, you can sell assets in the account and reinvest the proceeds without forgoing the tax advantage so long as you do not transfer money from within the account to outside of the account. As soon as you transfer money to e.g. your bank account, that money loses its preferred tax treatment and you are not able to transfer it back to the tax-exempt account beyond the annual limits (e.g. $7,000/year in 2024 for IRA contributions among people under 50).
60-day rollover – If a distribution from an IRA or a retirement plan is paid directly to you, you can deposit all or a portion of it in an IRA or a retirement plan within 60 days. Taxes will be withheld from a distribution from a retirement plan (see below), so you’ll have to use other funds to roll over the full amount of the distribution.
I would not encourage anyone to try to make clever use of this "float", but it's there.
This is not true. You actually have 60 days:
https://www.irs.gov/retirement-plans/plan-participant-employee/rollovers-of-retirement-plan-and-ira-distributions
I would not encourage anyone to try to make clever use of this "float", but it's there.