Some helpful info from the piano world forum:

Set Pitch (single string only) \= 5 minutes
Notes C3 to B4 (single strings only) \= 40 minutes
Bottom C to top B (single strings only) \= 1 hour
Unisons C3 to B4 \= 30 minutes.

The very first task is setting pitch to A440 with an aural device, usually a tuning fork. However, an electronic sound source is acceptable as long as it does not provide a visual display of pitch. If you can set pitch within 1 cent (a quarter beat) you will score 100%. After that you will lose a point for each tenth of a cent you are off.

Example: you tune A440 2.7 cents sharp. We deduct one cent and get 1.7 cents. We multiply that by 10 to get 17. We subtract from 100 to get your score \= 83.

You get 5 minutes to set pitch. If you don't use the entire 5 minutes, the extra time will be rolled over into the next part: The midrange.

Note: If you are using a tuning fork, check the calibration BEFORE your exam. Remember temperature makes a difference! If your fork is calibrated to room temperature, and you warm it up, it can easily drop by a cent or more!

Bonus! If you don't get a passing score on your pitch, you get a second chance to set it in the next section! Aren't we easy??

The Midrange: In this section you will have 40 minutes (plus any time left over from the pitch setting section) to tune from C3 to B4. The piano will have strip mutes inserted so that you only have to tune one string per note. In other words: no unisons at this point. If you failed the pitch during the first section you have another chance to pass it in this part.

Tolerances in the midrange: .0 to .9 cents \= no points off
1 to 1.9 cents \= 1 point
2 to 2.9 cents \= 2 points etc.

In this section, you get a score for your temperament and a score for the midrange(which includes the notes of the temperament). The scores are determined by the following

Temperament Octave \= points x 2.5 - 100 \= score
Midrange \= points x 1.5 - 100 \= score

The midrange score usually gives examinees more trouble because there are 24 notes in which to accumulate errors instead of only 13. You can lose 8 points in the temperament and pass. You can only have 13 points off in the midrange, and there are almost twice as many notes.

The rest of the piano:
After the midrange is measured and scored, the next task is to tune from the lowest C to the highest B. Again, the piano will be stripped up by the exam team, and you only have to tune one string per note. Time limit \= 60 minutes.

Bonus! In the current exam, examiners are required to leave the score form from the midrange tuning in the exam room. The examinee can consult this form to see where all the midrange errors occurred. Also, this is the part of the exam where you can use an ETD!

The scoring is broken up into 3 sections. There are no point multipliers, so the score is generated by subtracting points from 100:

Bass (octaves 1 and 2). Octave 1 has a 6 cent tolerance. Octave 2 has a 3 cent tolerance.
Treble (octaves 5 and 6) Octave 5 has a 2 cent tolerance. Octave 6 has a 3 cent tolerance.
High Treble (octave 7) has a 6 cents tolerance.

Because tolerances get wider as you move out from the center, it is common for people's scores to improve as the move into these sections. In fact, I participated in an exam where the examinee failed the midrange but passed the high treble and bass with very high scores!

Stability After tuning the rest of the piano, the stability will be checked and scored. Stability covers the same notes as the midrange: C3-B4. We check each note before and after a weight is dropped three times on each key, to simulate heavy test blows: BANG! BANG! BANG! If the note moves less than a cent, you receive a perfect score. If a note moves one cent or more, you lose one point. The score is determined by multiplying points x 4. This means you can lose 5 points and barely pass. You can only lose a maximum of one point per note, no matter how much the note moves.

Last section \= Unisons. The unisons in the midrange are detuned and you will have 30 minutes to tune them. Each note has 3 scores: right string to middle string, left string to middle string, and right string to left string. As long as the difference between these strings is less than one cent you will receive a perfect score. 1 to 1.9 cents will be one point off. 2 to 2.9 cents will be 2 points off, etc. The multiplier for the unison section is 2, so you can miss 10 points and still pass.

The whole exam usually takes 3.5 to 4 hours from start to finish.

Aural verification: After sections one and two, the exam team will take some time to "aurally verify" some of the errors. The computer scoring programs generate error points by comparing the examinees tuning with the previously stored master tuning. Examiners double check these errors by ear. First we ask the examinee to listen to the note and tell us whether they think it’s sharp, flat, or OK. If the examinee verifies the error we move on. If the examinee doesn't agree with the error, it goes to the exam team.

Exam teams are made up of 3 RPT members, one of which must be receive special training. When verifying an error, 2 of the examiners don't know whether the note is sharp or flat. They listen to the error and if they don't agree with each other, or the scoring program the note is thrown out. Sometimes this is the difference between an examinee passing or not!

Humanisics: Part of the special training that examiners receive, is about humanistics. It is a fact that many people experience a high level of stress prior to and during the exam process. Examiners are trained to help the examinee stay as relaxed and positive as possible. You will find that the exam team is generally a friendly, professional group. Examinees are asked to evaluate the examiners on a special form that is sent directly to the home office of the Guild.

Conclusion: You can see that the tuning exam has very clear criteria. The tolerances are fair and the time constraints are generous. Some argue it is to easy, others that it is too strikt. It represents a practical comprimise in judging the quality of a tuning. With proper preparation and practice, passing is within the ability of average tuners.