The reading section is by far the most important section of the TOEFL test. If you make a blunder here you will not be motivated enough already to go on to the next section, which is listening, an even tougher section. this section is not for the faint-hearted. So in the sense that you should be well-prepared for the following sections, you cannot pay enough attention to the reading section.
If you want to really concentrate on the reading passages, you should enter the room after, not prior to, most of the test-takers. If you start the section earlier than the others in, let’s say, a room that can accommodate 30 people, then, you are supposed to hear 29 others testing the microphone, asking the administrator questions, bumping into the table you are sitting at, and making complaints about the malfunction of the PC. I do not believe this is an ideal environment in which to concentrate on the work.
The reading section is, in a sense, a key to success in the TOEFL test. So important is the section that you should even be more careful in deciding when to enter the room. On entrance into the test center, your test already starts.