It's not really an exact amount of time, you can move it out of the dome once there is a sufficient root system. Initially you don't want TOO much light or transpiration will cause moisture to be lost to the air by the foliage faster than it can be replaced by the stem and later by the newly developing roots. That is the purpose of the humidity dome - to keep the air around the clones moist, the dryer the air the faster the leaf surface will lose moisture.

I place my cuttings into soaked peat puck starters after dipping them into generic powder rooting hormone. These are then placed into dixie cups with a sandwich bag over them. Every few days, I pull the baggie off to give the clone fresh air and then replace it. Once I see a few roots poking out of the sides of the peat puck, I know that it is developed enough to support itself so I pull it out then and pot it.

The actual number of days can vary - sometimes under a week, sometimes it can take a couple weeks.