What change in the interpretation of the First Amendment does this timeline reflect?

1914: World War begins.

1917: Charles Schenck distributes pamphlets encouraging U. S. men to resist serving the military.

1919: The Supreme Court rules that Schenck's action is not protected because it poses a "clear and present danger" to safety.

In times of war, freedom of speech may be limited more in comparison to wartime.

Explanation:

The Supreme Court ruling in Schenk vs. US established a new precedent in terms of free speech. If the speech in question did not pass the "clear and present danger" test, than it is not constitutionally protected.

The Supreme Court justices felt that Schenk's encouraging pamphlet to not join the US military would hurt America's chance of success in World War I. Therefor, it created a clear and present danger to the safety of American society.

In times of war free speech may or can be more limited than in times of peace is correct apex.