Did John Hanson declare that Thanksgiving should be the fourth Thursday of November?

No. The Continental Congress did proclaim a national day of thanksgiving each year during the Revolutionary War, but the date varied each year; the first was Thursday December 18, 1777.

In 1863, Lincoln declared that the last Thursday of November would be a day of thanksgiving. Presidents after followed Lincoln in declaring the last Thursday of November as a day of thanksgiving, but this was by Presidential Proclamation, and so while it became tradition it was not a matter of law.

In 1939 Roosevelt pushed Thanksgiving back to the second-to-last Thursday in November, in order to allow more time for Christmas shopping, and thus to stimulate the economy during the depression. Some states followed Roosevelt's proclamation, whereas others followed tradition. Some followed both. Since states were split in their observance, Congress passed a bill requiring Thanksgiving to be observed on the fourth Thursday of November, which could be both the second to last and the last Thursday of the month, depending on the year.