The time it takes to get a Pokémon egg from breeding varies based on trainer numbers and the specific type of Pokémon being bred. Check back at the day care on Route 117 every 256 steps to see if an egg has been produced.
The compatibility of the Pokémon also effects how likely it is to produce an egg during each 256-step egg cycle. You can speak with the Day-Care Man to find out how compatible the two Pokémon at the day care are. When you go back to check on your breeding Pokémon, if the Day-Care Man has moved from his default location, an egg is waiting.