I understand the thought. I looked at the rosy minnows churning in a petco tank for 22 cents each.
Consider how large the possibility is the results will be inconclusive or less conclusive than you hope.
Do you know LC50 NH3 data for those guppies? (I don't)
Erratic behavior is sort of in the eye of the beholder. It might be necessary to go to loss of swimming or death to be definitive.
Think about how high you are willing to go in total ammonia and pH and still consider it was a "fair test" of Prime in your eyes.
If all you are willing to do is go up to 5ppm total ammonia (what Prime explicitly says it is meant to cover), at pH 8.3, then compare the resulting
calculated NH3 - 0.398 mg/L NH3 to the LC50 data (which I don't know if we have) for the fish.
If you have to go to something like 4 days, then the complications mount dramatically. You have to think carefully about feeding, or it's partially a starvation test.
If you feed, you introduce the possibility of heterotrophs using the carbon and lowering NH3 by some amount. You may need to do once or twice daily 100% water changes at the target ammonia and matched pH to be certain you are actually maintaining those values.
Newly bought fish bring diseases etc. Those diseases can affect an entire tank. I'm fairly confident an experienced reefer can recognize fish disease, but if the ammonia stress persists for days - disease may be a manifestation of the stress.
edit: I found some LC50 NH3 data.
From EPA guideline
[pdf]
"Rubin and Elmaraghy (1976, 1977) tested guppy (Poecilia reticulata) fry
and reported
96-hour LC5Os (Table 1) averaging 1.50 mg/liter NH3; mature
guppy males were more tolerant,
with 100 percent survival for 96 hours at
concentrations of 0.17 to 1.58 mg/liter NH3."
That seems to put them entirely out of range for a definitive test within your bounds of what's "fair" to Prime. So I'd say this test is not worth attempting.
I think this is a general problem - most anything we'd be sorta OK with killing by ammonia is likely too tough to do so within the explicit amounts that Prime claims it protects from.