The length of a video is determined by the plan that you have. In general, videos can't be more than longer than 300 minutes unless you are on the Network tier. The Network tier does not have a limit. But you need enough video creation time to make a 300-minute video with the Creator, Influencer, and Agency tiers.
The Creator plan would be limited by the amount of time you have left in that plan for the month. For instance, the Creator plan comes with 30 minutes of video creation a month. If you only have that 10 minutes left, then you could only make a 10-minute long video. This would be the same for the Influencer and Agency tiers as well.
Though Wavve does not have a limit on how long videos can be (other than limiting videos to the number of minutes on your account), we suggest not making videos more than 120 minutes long. The longer a video is, the more of a chance it may fail to render due to the number of computing resources required to generate that video from scratch. If a video fails to render, though, that time will not count against your account and you can retry making it.