As native English speakers I think we tend to relate pretty easily with the expression {} or , meaning to have free time or to make/spare time. The meaning in question is similar but not exactly the same. The and the lack of the direct object kind of obfuscates the real meaning. Indeed, it could be read as , but that would mean he essentially cleared up 3 weeks to be less busy. Instead it's referring to the website/place where he usually is: . This usage refers to being away from somewhere. Literally it means that he "emptied" the site, referring to his not being there figuratively.
On alc we see some examples of this:
>
> be away from home __ days
>
>
> stay out all night with no questions asked
>
> 10
> leave a room for __ minutes
Hopefully this is clear! It's just a literal idea of leaving a place vacant.