How soon after updating expire_logs_days param and restarting sql will old binlogs get deleted?

Question

MySQL 5.1.x | InnoDB | Windows

My mysql data directory is starting to fill up with bin logs.

I currently have the following settings configured in my windows mysql server:

[mysqld]
log-bin
server-id=1
binlog-do-db=foodb1
binlog-do-db=foodb2
expire_logs_days=25

I'm planning to change the expire_logs_days setting to expire_logs_days=10 and bounce the mysql service. How soon after making this change can I expect the old bin logs to get clear out.

Is this only done as part of a nightly scheduled task? Or should this be immediate?