Take them in order. When a gain comes through a partnership and the partnership itself hasn't made a deferral election, the partner generally has more than one possible start date for the 180 days, including the partnership's tax year end and, in some circumstances, the due date of the partnership return without extensions. Which one applies to your K-1 depends on the character and timing of the underlying sale, and that determination belongs to your CPA in writing, not to a forum.
On which rule set governs: the relevant event is when you make the investment into the qualified opportunity fund, and separately whether the fund's property sits in a designated zone at the time it acquires that property. The One Big Beautiful Bill Act made the incentive permanent, replaced the fixed deferral end date with a rolling five-year deferral for investments made after 2026, tightened tract eligibility, and imposed reporting obligations on the funds. The year your underlying gain arose sets your window. It doesn't set the regime your investment lands in.
On signature versus wire, the investment is the contribution of cash or property to the fund in exchange for an equity interest. A signed subscription with no money moved generally isn't a contribution, and I'd treat any sponsor who tells you otherwise as a sponsor whose documents you need read by counsel. Ask them for the exact mechanic: when is your interest issued, when is capital due, and what happens if the acquisition slips past your window. That last one is the trap. If the fund's first close moves by ninety days and your 180 days closes in between, you pay the tax and you're still contractually subscribed.
One more at the fund level. A QOF is tested on its asset mix twice a year, so a fund holding subscribed cash without qualifying property can incur penalties, which reduce the pot you're invested in.
