There is not a "fast" way to get cubits unless you win a big coinflip or trade items for cubits. The best way in which I got to nearly 65 cubits in a couple of weeks was buying them for mana! Mana is relatively easy to get on Olympus, therefore being half into the season and having almost 12 million mana, I was able to keep on mining to get more while buying 0.1-0.5 at a time at a smooth rate. It wasn't a day's process, but overall it was the best and most efficient way of obtaining them as it wasn't all one big purchase. Players won't sell them in huge quantities, therefore even though I would only buy around 0.1-0.8 at a time, it added up quick! Hope this helps!