Until they satisfied the profit that they targeted before converting into fiat.  How long they hold?  Every one of us here has a desired profit they want, if you are too much greedy, it could probably take a years before you will have a good result. 

Most people now prefer to hold than use in trading their Bitcoin or spending this in any transaction as a payment method, if you are trading it in a short term, you should also consider the fees, instead, while you are not holding and sell at one in a time to save some fees.  That's why there are few people who invest in Bitcoin and hold it for a long time because they think that Bitcoin is a safe haven after all.