[raghavtoshniwal]

Adding a space after 'before:' works.

Edit: sorry, this invalidates the filter. My bad.

[coltonweaver]

Spaces make the operator invalid, so it’s not actually filtering by date in that case: https://support.google.com/websearch/answer/2466433?hl=en

“ To narrow your results in specific ways, you can use special operators in your search. Do not put spaces between the operator and your search term.”