It is far better to sit at the table and observe it.
I mean, it s a cash game, you are in no rush at all. Usually you buy in for ~200bbs.
At least it's a better view of players, how they behave, you can closely see when someone shows a card, a hand.
At the same time, observing the table for half an hour then sitting, I would feel discomfort - being new to the table, only just getting the first hand etc.
If I was at the table for half an hour and folded every hand, I feel comfortable, already picked up on the dynamics of the game, on the pace, probably figured a couple of players along the way.