Problems with microsoft forms

Question

Recently I use Microsoft forms to make online quizzes. I have faced many problems recently:

1. Last month, one of the students couldn't open it, she was receiving the same window that she cannot get in.
2. This month, the same problem happened with two students. I programmed it to open and close at specific times (I gave 40 minutes between them), one of them couldn't open it, the other could open it about half an hour later, then it closed automatically later to the programmed hour (but less than 40 minutes).
3. I repeated the exam for the first one, and changed the settings, I removed the timer, it was open. But she faced the same problem and opened about half an hour later.
4. I repeated it to the second student, without a timer too, but he couldn't make the submission, so he sent the replies as screen shots.

Some people say it is better not to set a beginning time, and to publish it just with ending time. Others say it needs a strong internet. Others asked me to check the laptop hour if they match, but I don't have a problem with it.