How long time PCQ reserves bandwidth for substreams?

How long PCC reserves bandwidth for substreams after last user activity?
There is a RouterBox 5.4 connected to external 30Mbit/s channel, shared using PCQ to bunch of masquerad’ed clients:

/queue type
add name="PCQ_download" kind=pcq pcq-rate=0 pcq-classifier=dst-address
add name="PCQ_upload"   kind=pcq pcq-rate=0 pcq-classifier=src-address

/queue simple
add burst-limit=0/0 burst-threshold=0/0 burst-time=0s/0s direction=both disabled=no \
    interface=all limit-at=0/0 max-limit=30M/30M name=queue1 parent=none priority=8 \
    queue=PCQ_upload/PCQ_download target-addresses=10.0.0.0/8 total-queue=default-small

It seems that 30 clients have gets the fixed 1mbit/s substreams, even they surfing websites only.
So my current queue configuration should work good for torrents, but not so good for websurfing.
But each surfer has long inactivity periods when his bandwidth can be divided between another surfers.
Is it possible to utilize common bandwidth more efficiently?