It sounds like your daughter is experiencing really strong feelings around transition times. From the ages of about 1 - 6 years old children are experiencing a lot of brain growth, especially in their middle brain which is the emotional center. This means that your daughter needs a great deal of support around the big feelings that she is having around the difficult transitions, which, by the way, are very difficult for most small children. Try this: Let her know ahead of time that you and she will be doing something different, e.g., "in ten minutes we are going to brush teeth . . . okay, it's been about 7 minutes so in 3 minutes . . . " When she begins to get upset, notice that she is having these feelings and acknowledge it out loud to her. "I see that you are really angry (frustrated, upset, sad) and I'm wondering if you are not wanting to leave because you haven't finished your game (I'm wondering if you are really sad because you will miss mommy, etc.)" Hold her if you can, let her have her feelings and give her empathy. this is crucial because when you connect with her like this, she will know that you "get it." She will still have to make that transition and she will know that she has a parent that loves and supports her. "Hold the limit, hold the feeling" is kind of a mantra in our house and it means that we are able to emotionally support our child, be empathetic and also hold the limit that we've set. Try it a few times and see if the 20 or 30 minutes doesn't go down to 5 or 10.