You are part of a team designing a new app that lets people know whether their teeth need whitening. Your group has responsibility for the color variant programming. It will take you two weeks to complete the task. If your finished project isn't done in six weeks, the next part of the app won't get done in time for the launch...very bad, very expensive situation, if it happens.
In this case, the float time for your part of the project equals four weeks. Float, or what's sometimes called "slack," represents the amount of time a task can be delayed without triggering a subsequent delay to some other task down the line. It's part of project manager lingo that lets the people in charge know how much they can mess around before getting in trouble.
In the case of the teeth-whitening app, you have a two-week project that must be completed in six weeks. So, theoretically, you and the rest of your group could spend the next four weeks napping and playing ping pong in the office, and still get your part of the project done on time. Thus, four weeks represents your float time.