Don't think you can over oil it, the down side that if it was over oiled it would 'sweat' out of the wood and into the strings/fingers, maybe making the strings go 'dead' prematurely or make your fingers slippy,.
I guess if you live in a hot dry climate 4 or more times a year is suficient, heated/air conditoned houses will have the same effect.
Then there is humidity, whilst I was on holiday in florida from the UK, I talked to a bass player who used a modulus if he played outdoor gigs as the humidity played havoc with his jazz bass neck.
There is a thread about it all somewhere here