My bluetooth mouse automatically disconnects from OS X after 5 min or so of idling.
Left/right clicking the mouse will wake it and automatically reconnect after 5 sec or so but it's clearly a hassle.
Is there a way to disable or extend the idle timeout?
Depends on mouse brand and which driver you use. If it's some universal mouse,you might find it in settings,but usually,on newer Apple computers,the mouse drivers are optimised for Apple trackpad and the Apple Magic Mouse.