First, make sure that you are reporting the income shown on the Schedule K-1 (Form 1041) on the correct year's individual tax return of yours. The income is reportable on the individual tax return for the year that contains the end date of the estate's income tax year. Receiving the Schedule K-1 in August or September might mean that the estate is requesting a filing extension each year or it might mean that the estate is using a fiscal tax year rather than a calendar year.
Assuming that you are receiving the Schedule K-1 that late because the estate has requested a filing extension, it would be reasonable to file your tax return with an estimate of the amount that will be reported on the Schedule K-1, then amend later to correct that entry (still, if you've already received the money you should already know the actual amount; that money should be paid to you no later than 65 days after the close of the estate's income tax year).
You can also manage your tax withholding and estimated tax payments so that, after factoring in the income from the estate, you anticipate a small refund and just request a filing extension for your individual tax return, giving you until October 15 to file. By doing so, there will be no real downside to you filing on extension.
