If you have other capital gains, the capital losses go against those first. Only if $-3k in losses remains can you subtract it from income. And if you have even more losses, you carry them over to next year. If you have too few capital gains again next year, you could again subtract $-3k from income.
Tax loss harvesting now vs later only matters if you're trying to time which years you have capital gains. In the absence of a specific plan, I'd go with selling at a loss this year. Well, Monday to be specific - last trading day of the year.
Even if you're paying an expense ratio on another ETF, consider you only have to hold it just over a month (to avoid a wash sale). So an ETF that charges $15/year per $50,000 (0.03% expense ratio) will only cost $1.50 to hold for 36 days. And from that $1.50 you gain thousands in taxable losses, and save hundreds on taxes. You pay a few dollars to get a loan for hundreds of dollars.
It's also worth checking which ETFs are $0/trade at your brokerage. Fidelity and Schwab have different groups of funds (but Vanguard charges $0/trade for most ETFs now).