Unless you want the challenge and satisfaction of doing it yourself, why wouldn’t you get an existing product like one made by Toro?
You’ve answered your own question.
Here is an Automatic plant watering system using Arduino UNO:
The same thing can be implemented using a Raspberry Pi Pico. Like the Pico plant waterer:
For turning on two hours twice a week, you can configure an in-built timer or interface an RTC.