You can change how often Adaptivity (and so noise level) is calculated, it's in the devel debug section. Do note, though, that the default of 5 has been chosen deliberately (so that things are efficient), but the option to change it is there - personally, I only change it for debugging purposes (hence the name of the section!) when wanting to watch closely what noise is doing each pass :)
Of course not quite the same as having a button (but why would you want that btw? Could you explain more as to why that would be useful for you?)
Thanks!