The healing process can be a bit longer and more complicated than most other piercings. Daith piercings to be a magnet for dirt and germs that are around us. And it also requires more attention simply because it is a larger wound than a thin cartilage piercing. It is imperative that you keep it clean and strictly follow your aftercare instructions. As with all ear piercings, I also recommend that you avoid contact with makeup, hairspray, and perfumes; you should also change your pillowcase every day and cleanse your ear after talking on the phone or wearing earphones, earmuffs, etc.
Jewelry size and gauge needs to be determined by your piercer, and it will depend on the size and thickness of your cartilage. Proper sizing is really important, especially with cartilage piercings, because it's so easy to damage the cartilage and permanently disfigure your ear if it's not done right.
As with all cartilage piercings, in a perfect world it should only take about 4-6 weeks to heal, but most people encounter some kind of problem(s) along the way. Those setbacks make most cartilage piercings actually take 3-6 months to finally heal completely. It just takes persistence and patience to get to that point. Don't give up if you experience problems - they'll eventually go away.