I've done it both ways. In person and on the app. On the app, you can check in 20 mins before and it will give you instructions as to what to do, and will tell you when your table is ready. If you have it set to send you texts, you'll get a text (that's my favorite way because I seem to get that faster).
I've also checked in at the podium. On my last trip, the app wouldn't let me check into Coral Reef with just me, so I went to the podium. The awesome cast member took care of everything, and I got a text when my table was ready, which was only 15 mins after I checked in.