How long for this cement smell to go?
The odor is a function of the drying process. Some moisture is chemically bound to the cement, but some remains. The dryer and breezier the area is the quicker it'll disperse. We can't really say.
It is odd that the cement is so smelly that you notice it. A new basement slab smells like fresh concrete for weeks or years, but that small patch shouldn't really be noticeable if there's any ventilation at all.
You could coat it with a sealing primer, then paint it to help block the odor.