it depends on the projects, there are ICO that sold out in less than 24 HRS like the Hwllo Coin, an there are also ICOs that didn't reach its cap like the NotaryPlatfrom, and the normal duration of ICO would last about a month, the status of ICO depends on the team and their campaign strategy if it is well exposed then that ICO will sell like hotcakes.
Yes all ICOs have differences in the duration of their time. it all depends on the target of the ICO and also interesting what token to be traded. If the ICO is interesting Then will bring a lot of investors and we can see that the coin / token will be sold very quickly. You can see more and more investors on an ICO then the chances of ICO being successful are getting bigger.