Regarding water flow rate for in ground irrigation system

I have a professionally installed in ground irrigation system. I had the installer add two extra zones for possible future expansion to water shrub/flower beds. I am now ready to hook into one of the pvc pipes for one of those zones. My question has to do with determining my water flow rate to determine how many sprinkler heads I can have. I measured the flow rate from my outside faucet through a 50 ft. hose. (mainly because my faucet pointed kind of sideways instead of down and I figured it would be hard to hold a 5 gallon bucket in front of the faucet without a hose.
Would testing the rate through a 50 ft. hose reduce the flow and the time it took to fill the bucket?

I have a separate water meter and inlet pipe to the irrigation system. I believe the main lines of the irrigation system are 1 inch. Would my actual flow rate be higher on my irrigation system than the outside faucet on my house?

 

I assume you are using "city" water since you mentioned a meter. The flow rate needed is determined by the number if sprinkler heads and the type. Using a garden hose is fine to get a handle on what you have. A hose offers more flow resistance than a PVC pipe. The unknown is the pipe sizes. Pipe size from the meter to the backflow device, to the zone valve and then to the sprinkler.

Generally, the system would be feed by a 1" or 3/4" pipe, the zone valves can be 3/4" or 1". 3/4" pipe minimum would feed the zone and then branch off with 1/2" to the sprinkler head.

https://school.sprinklerwarehouse.com/design-and-install/