Smooth knob tailed gecko cage size

Hi all, im going to be getting a smooth knob tailed gecko some time soon, and I have a cage that's 330mmL x 380mmD x 330mmH. Just want to know if that's big enough for pair (male and female or 2 females).

(edit) also, on all the care sheets I've found, they don't make it clear exactly how often the cage needs to be cleaned (not including daily spot cleaning) and how often the sand needs to be changed. Would once a month be enough?
thanks in advance for any advice

- - - Updated - - -

Nothing?

- - - Updated - - -

Still nothing?

Still nothing...

I'm not going to answer the size question as I'm not entirely sure myself but with the cleaning I can. As a lover of sand as a sub for arid terrestrial lizards I can tell you a lot about the stuff. I do daily spot cleans and to a full clean out and replacing of the sand every 2 months. If you want to go through the effort you can clean and reuse sand, not worth unless your on a budget or your really bored haha

Thanks crazynut for the info, much appreciated