Hi ic,
You didn't mention what type of sprinkler heads you have, but I recommend just removing the nozzles and cleaning the head filters and nozzles and see if that helps. Check if the throw improves if opening each valve manually. If all the heads are all on one zone or several zones. If all zones throw less you might have a pressure drop in your mainline. Check your faucet pressure. Has the pressure in your house changed? Anyway there are many of possibilities. The more info the better. Buy a pressure gauge from the hardware store that goes on to your hose faucet($15) and monitor your pressure. Let us know the results and we can help further. Aloha

Thanks for the reply.
I have those common pop-up heads. each row (3-5 heads) is under different valve (zone).
I shut off some of the heads in the weakest zone and the ones that were open seemed to shoot the water further. So I assume it has to do with pressure...
I will definitely take a look to the head filters.

Try changing the start time back to 8:30AM and see if the system works better. There might be a water pressure issue at 6:00AM due to demand in your house or neighborhood (like too many people taking showers or watering lawns at the same time).