On every Vieworks widget, there is a countdown timer seen in the top right hand corner of your promotional video as seen below. The default unlocking percentage is set to 75%, this means that the video will start counting down from the 75% mark until the user may claim their perk successfully. E.g. if I have a 1 minute video and leave the countdown timer as default, it will start counting down from the 45 sec mark, but if I select 100%, then the viewer may only access their perk after 1min has elapsed.
The countdown timer is particularly useful if you have a longer video, so that you can decide when is the best time frame you want your viewers attention for, before they qualify to get their perk.