Will I be able to change it during a busy shift at work?

One of the best things about a cup is that they can hold up to 3 times as much blood as a tampon, so you can go longer between changing/ emptying. And depending on how heavy your flow is can be worn up to 12 hours at a time. 

When changing it, you more you do it the quicker and easier it becomes, so you can easily do it in your speedy loo break.