How long will it take for a silkie x plymouth rock to hatch?

[Star428]

Plymouth rock is the hen, silkie is the roo
Not sure how it works when it's a mixed breed? Can't even find how long it takes for plymouth rock to hatch...

 

[MGG]

Plymouth rock is the hen, silkie is the roo
Not sure how it works when it's a mixed breed? Can't even find how long it takes for plymouth rock to hatch...

All chickens take 21 days to hatch. Bantams take a bit less time in some cases if your temperature has been perfect the whole time, they can hatch on 19-20 days. But if it's mixed especially 21 days is how long it should take to hatch.
Do you have a calibrated thermometer and salt tested hygrometer in your incubator to make sure the temp is accurate?