When will the election be declared? Look at time zones and States “solid” for Biden/Harris. In the East - generally the first to report results - that means the votes of 90 electors. Using postal abbreviations: VT 3, NY 29, MA 11, RI 4, CT 7, NJ 14, DE 3, MD 10, DC 3, ME 2.
Other States in the Midwest and West are solid, but report later and total 98 electors. IL 20, WA 12, OR 7, CA 55, HI 4. That means Biden/Harris have the votes of 188 electors. They need the votes of only 82 electors and they win.
States in which the margin is very solid for Biden/Harris and that are far enough East we might have their final tabulations relatively early: VA 13, MI 16, WI 10, MN 10 = another 49. A bit more west: CO 9 and NM 5 where Biden/Harris leads are double-digits.
That puts them 18 away. Consequently, if any State that has more than 18 electors - PA, FL or TX - flips blue, the night is over. If any combination of States totals 18, ditto.
In 2008 I knew then-Senator Obama had won when I saw reports from a couple of counties here in Indiana that showed him breaking even. In those counties, a Democratic candidate only should have pulled 25%.
There might be litigation, but I think the margin of victory for Biden/Harris will be so great that litigation will prove silly. This could be called quite early.