Question

How long does it take for an egg to appear at the daycare?

Comments

it depends on ivs and how well pokemon get along and genders ect i think

Answer 1

None of these other answers are fully correct so I thought I should add my own.

Whether or not an egg is produced is decided ever 256 steps you take, so if you're standing still, nothing will happen. You can't just wait. Whether or not an egg is produced is based on how well the Pokemon in the Daycare are. A detailed list of what the Daycare man/lad/lady say about your Pokemon that can help you determine this chance can be found in my source below. Aside from what is said about your Pokemon, the chance an egg has to appear every 256 steps can be determined by what two Pokemon are being bred:

• If the Pokemon are the same species and have different OTs, the chance is 70% (88% with the Oval Charm)
• If the Pokemon are the same species and have matching OTs, the chance is 50% (80% with the Oval Charm)
• If the Pokemon are different species and have different OTs, the chance is 50% (80% with the Oval Charm)
• If the Pokemon are different species and have matching OTs, the chance is 20% (40% with the Oval Charm)

It should also be noted that these percentages are different in Generation II. The circumstances and correlating percentages for these games can be found in my source below.
Source

Answer 2

if the 2 breeding pokemon are getting along(if you ask the old man, he'll tell you)every 256 steps a 50%chance.

Answer 3

It really depends, because once I walked outside of the day care centre and the old man told me that my Ninetails was already holding an egg.

Answer 4

Once I was breeding Mudkip on White and the old man said I had an egg. Well I took it from him and as soon as a reached the bottom of those little stairs to the black path (about 5 steps) there was another egg. Yet with the same pokemon in the daycare I rode around on the bike for at least 10 minutes before there was another egg. So, even if they are getting along, there are a lot of different time spans between eggs sometimes.