With your bioload you need to keep p on the waterchanges, with a light load and a balanced tank you can go a long time between them, the ultimate answer comes from your water tests, if you test at least once a week and your ammonia and nitrites stay at zero with nitrates below 20 ppm you can put it off but even then you are playing russian roulette, eventually something will go wrong and when it does it can happen fast. Why risk it?