Difference MP4559 and MP4560 on startup

I am successfully using an MP4559 and had to replace it with an MP4560 due to component availability.
This also works as expected, but there is an unexpected difference.
As you can see from the picture, the start-up time of the MP4560 after applying the supply voltage is 7ms, for the MP4559 this is 2ms.
I cannot see this difference from the data sheets, but would like an explanation.

Additional Info: We do not use the EN pin, so this pin ist not connected

Thanks for your help.