How long can Zoe keep a stolen spell before it expires?
And: Is it influenced by level or CDR, please?
And: Is it influenced by level or CDR, please?
60 seconds according the wiki, and I believe it is a flat 60 seconds because you want to hold them longer rather than shorter.
Collecting a Spell Shard allows Zoe to activate Spell Thief within the next 60 seconds. She can replace her current Spell Thief active by issuing a move command directly on another Spell Shard.