Doesn’t youtube use https now, so https wouldn’t be blocked as the site blocker uses the web shield functionality to display the blocked site info page. The reason for this is the web shield currently doesn’t redirect/monitor https traffic.

I tried a block on both the examples you gave and mine were able to block, see example of the URL strings input in my settings.

The first example sets a wildcard to save typing the http www bit and would also work in blocking sub-domains of that site.
The second example uses the full url and avast tags the trailing * to the end of the url string.