You might simply assume that the best shift to cheat live casinos is the swing shift because that's simply the busiest shift for casinos. While that is indeed true it doesn't always mean that professional casino cheat teams prefer to work the swing shift as a priority. Although it is usually best for cheat teams to work busy casinos simply to blend in better and camouflage their cheat moves, sometimes the busy casinos prove burdensome for organized cheat teams, especially when they consist of three or four members working to do the moves. They may find it nearly impossible to secure their places at the tables. This is especially true of roulette wheels where three or four cheats are needed to work well-orchestrated moves. Other slower times such as the graveyard shift offer cheat teams a more relaxed atmosphere where pit personnel and dealers are friendlier and less on-guard for cheating. When moves are very strong and don't require more than one or two team members to pull them off, the graveyard can be the ideal shift.
So really there is no specified "best time" to cheat casinos if you are a good cheat working alone or with a team. It depends on many factors including move-difficulty and room required at the target table. If you are not such a good cheat it is probably better to work the crowded casinos in as much as you can disappear quickly into the throng if you have a problem and need to get away from the pit personnel's view.
One negative about empty casinos for ALL cheats regardless of number and skill: If you have to get the hell out of "Dodge" on the quick and bolt across the casino, you are going to stick out like a sore thumb and have a heck of a time getting away!