I'm looking to make a plant watering system that waters plants periodically, maybe once or twice a week. Would the delay function be suitable for this or is there some way to make a more accurate timer? Not that it's really necessary, but I would like to be able to have it accurate at least down to the minute, just for the hell of it. Would an oscillator or a timer chip be suited for this?
Down to the minute is not accurate.
The arduino clock is accurate to about 30 ppm. If you want more than that then use a real time clock module.
You can use delay but something based on the blink without delay would be better.
I think I'd still be inclined to use a RTC. It's such a cheep device but would keep your time schedule in line with the real world. Bearing in mind, that without it, in the event that your device is switched off, for even a moment, It will lose track of where it was in the timing cycle.
You'd only need two interruptions in any week (could happen if the weather causes a power outage), your plants would go unwatered for maybe 10 days.
For sake of the extra couple of quid you'd have peace of mind.