Looks like it's possible to get it from another uImage:
$ file uImage
uImage: u-boot legacy uImage, Linux-5.4.242-letux-lpae+, Linux/ARM, OS Kernel Image (Not compressed), 5380376 bytes, Thu Apr 27 10:55:17 2023, Load Address: 0X80008000, Entry Point: 0X80008000
1685000934
Not to mention that...