lit. you may go undetected during the new moon, but at full moon you'll be found out (idiom); fig. you can't put it off forever; sooner or later you'll have to deal with it
trad. 躲得過初一,躲不過十五
Also written 躲得過初一,躲不過十五【duǒ de guò chū yī , duǒ bù guò shí wǔ】