wood and strings can be a little unreliable when it comes to maintaining a precise set of gaps and distances like the ones required when setting up a bass
all sorts of things tend to effect it temp,humidity,stress from playing etc but how often do you tweak your action/neck relief/tuning etc and how often do you check it too?
myself i check the neck relief everytime i pick the bass up as i believe its the main thing that makes my bass as playable as it is however i only check the bridge saddles when replacing strings and sometimes i will go months without checking the tuning only to find my strings have all gone flat
how often do you tweak?