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To have any realistic hope of this working... you have to have a REALLY short garden hose.

Generally speaking, irrigation systems use 1" and 3/4" pipe. A garden hose is going to be about equivilent to 1/2" pipe (note that a 3/4" pipe can carry twice as much water as a 1/2", and a 1" can carry twice as much as a 3/4"). That means the garden hose is going to be VERY RESTRICTIVE and pressure losses will be HUGE.

As an example, if we were talking about trying to push 9gpm through 1/2" PVC pipe, the pressure losses would be OVER 25psi for every 100' of hose. Add to that the fact that the spicket is likely feed by the equivilent of a 1/2" copper pipe. That copper pipe will have over 12psi of pressure loss for every 100' Then add all the pipe between the street and the point where the 1/2" like breaks off from the water main. The other issue is if your house has a pressure regulator (which it likely does if your city water has an incoming pressure much over 50psi), the odds are that one spicket is before the pressure regulator, and the other is AFTER the regulator. So that likely means that the spicket that is AFTER the regulator STARTS at 50psi, and then you have all the pressure losses from there til the water comes out the hose.

So as a GROSS estimate, regardless of what you got from the bucket test, you likely won't have more than about 5gpm to actually work with. From what I can see regarding the heads you plan to use, each head at a 180 degree spray pattern looks to use about 0.5gpm. So I would estimate that you could expect to properly run a maximum of 10 of those sprays if they are all 180 degree spray patterns.

Granted that these are gross estimates that makes some general assumptions about your plumbing. But in general, there is a reason irrigation systems are not set up to run off a hose spicket. The generally instead tie into the mainline a close to the meter as possible, and then use 1" pipe through most of the system to help minimize pressure losses.

Maybe... the only way to know is to find the exact details on what flow rate is needed for the exact nozzles you are going to use.

As an example, I looked at Rainbird 15 Series MPR Nozzles assuming a working pressure of 30 psi (i.e. after pressure losses through pipes and the garden hose, you still have to have 30psi left over). If you were running three of these nozzles with a 180 degree spray pattern, that would be using 1.85gpm per spray head. Three of them would use 5.55gpm. With enought starting pressure and a very sort garden hose, that would be doable.

But if you used three of these Rainbird nozzles, they would use 3.7gpm each, or more than 10gpm total. No way is that going to work.

Now an alternative that very well might work is to use MPRotators. They are sort of like rotators, but it's a nozzle you place on a typical spray body like the Rainbird 1800. http://www.sprinklerwarehouse.com/Walla-Walla-MP-Rotators-s/781.htm These typically use less water flow than normal nozzles. As an example, a 2000 series at 30psi with a 360 arc (full circle) only uses about 1.25gpm each. That would make 3 using 3.75. That might be very doable with a short hose.