It is not easy to say exactly how long the boost will last. It depends on what package you choose, which country and what time at day/night you boost.
How your boost work in terms of speed and visitors :
Regarding how long it lasts, that's one area we see cause a lot of confusion. The boosts are not time based. Each package and option has a certain amount of popups you are actually paying for, and we send it as fast as we can. The speed depends on what package and what time of day you do the boost. If it's during slow hours of the day it takes longer to deliver the amount of popups.
Quickboost will send the guests as fast as possible, and can get you to 1000 guests in just a few minutes, (since the traffic is comming from all over the world). How long they stay there depends on how good the model is to keep the guests there. So when you start the boost, it's important that you are aware of that and put extra effort into your show. We also recommend enabling guests to chat in the room so they can communicate with the model.
Other packages like English boost or other language boosts will last longer, and not send the traffic so fast, (since the traffic is comming from only English speaking countries). So it's a more stable flow of traffic.
If you choose USA boost, the boost will last longer when the Americans are sleeping, then the boost will do if they are awake.