It doesn't necessarily mean that the longer the ICO the better it gets, if the project is poor it will remain poor all through, and will make no difference no matter how long it takes. It however takes time to raise the targeted amount of money needed for the ICO or realize the target sales hence the length of time taken
I get yours is the long time does not remain that the project will reach their goal but its seems like the project shows its weakness.
If the token sale hold for longer or even exted again and again to get their goal, but in other side investors will think that the project is inconsistent so we need to stay away from this project.