No, you cannot directly access from Laptop to OpenSprinkler, you need Router AP.
You can using WiFi thetering with your smartphone, then connect OpenSprinkler to your smartphone, then access it with OpenSprinkler App from your smartphone.
or Conect your Laptop to your smartphone if you want to access it with your laptop.
Btw, if you want to build a sprinkler system by your self, you can try to build ESPrinkler ( https://github.com/n0bel/ESPrinkler2 )
It have SoftAP Mode, so you can access it from your laptop without Router AP.
I Have built ESPrinkler, but i’am not using it anymore, right now i use a modified OSBee.