The answer was (likely) given in a study of 9 Japanese men who were put on 125 mg of testosterone enanthate.  For those who don’t know, testosterone enanthate has a very similar dosage and half-life profile to cypionate and so the results from the enanthate study will apply to cypionate as well. The testosterone levels posted by this study are very revealing: **
**NOTE: These are estimates based on my read of a chart within the study.
- Day 0: 400 ng/dl
- Day 1: 750 ng/dl
- Day 2: 720 ng/dl
- Day 3: 690 ng/dl
- Day 4: 650 ng/dl
- Day 5: 750 ng/dl
Notice also that the peak does seem to occur on day 1 and steadily decline a bit for a few days after. However, you’ll notice that day 5, for no apparent reason, shoots back up to the peak or very close. (Day 6 and beyond are much lower – something I discuss in my page Should Testosterone Cypionate Be Taken Weekly or Every Two Weeks?)
The reason for this could also be that some guys are peaking on day 1 and some on day 2 and some on day 3. Regardless, I think the key thing to notice is that the testosterone values were all within about 15% of each other for the first four days and, therefore, you are unlikely to experience any substantial difference during those days. This is especially true when you consider the fact that the average young male experiences a diurnal (daily) cycle of about 35% from morning to evening testosterone levels. (See my page on The Daily Cycles of Testosterone for more information.)
Another point worth making is that day 5 shows the variability currently inherent in testosterone testing. Unfortunately, it is simply not that exact and depends on many factors. Cornell urologists recently outspokenly criticized the lack of standardization and consistency in lab testing:
“Despite advances in technology, inconsistent laboratory practices, among other issues, leads to unreliable blood test results. “In some cases, testosterone (T) levels, tested on the same day from a blood sample taken from a single patient, differed by as much 30 percent from one lab to the next,” says the study’s lead author, Dr. Paduch, a urologist and male sexual medicine specialist at NewYork-Presbyterian/Weill Cornell Medical Center and associate professor of urology and reproductive medicine at Weill Cornell Medical College.” 
If you’ll notice, the above underscores yet another reason to rely on symptoms as much as lab results!
The maximum level that I have seen at least – at least from what I have seen with most HRT clinics – is to not go over about 1200 ng/dl. This is considered the highest “physiological” level that you’d see in a healthy, young male.
Of course, to find your trough total testosterone, you simply get a lab read on the day you go in for your injection. However, if you want to find your maximum testosterone, do you test on day 1, 2, 3 or 4?
My answer, based on the above, is that it probably does not matter. Basically, if you look at the data above, the day 1-4 values are all within the range of the typical lab’s accuracy anyway. So there simply is no need to stress out over it and you can likely get a read on day 1-3 and be just fine.
CAUTION: There is an exception to this. Men with low SHBG often “clear out” hormones notoriously rapidly from what I have seen. So if you are a Low SHBG Man, then you may probably want to test on day one. Low SHBG is SHBG < ~15. Talk to your doc, of course, and get his/her practical experience (assuming they even know anything about the subject).
1) Endocrine J, 2006, 53(3):305-310, “Hormone Profiles after Intrasmuscular Injection of Testosterone Enanthate in Patients with Hypogonadism”, https://www.jstage.jst.go.jp/article/endocrj/53/3/53_3_305/_pdf