Yes, patience. Has he been in daycare before? This might be a factor. I have had that exact situation. He was 26mo, never been in daycare, never away from mom but by the end of the first week, it was like he'd always been here.
The mom sneaking out is not something I recomend. Leaving soon after dropping off, yes, but the sneaking out could feel like abandoning. She should say good bye and as hard as it will be for her to watch him cry, I believe it is the best thing for him.