Without seeing what's going on down in CWT::Site_DB, it's hard to say.

A flag goes up when I see code that mixes direct queries with queries that are abstracted away behind classes. It's hard to get a grip on what your connections and statement handles are up to unless they're either all exposed, or all abstracted away behind well unit-tested classes (or at least that's been my experience).

Scanning the code, it shows that you're starting off with an id, querying first to get the corresponding username, then querying and iterating over a session table to look for (a non-expired session?) with the same username

Is that something you could arrange to do in a single query, using JOINs or OUTER JOINs?

Also, it's generally bad form to "SELECT *" in production code unless you're going to use all of the fields. Better to name the field explicitly.