Well since at the kernel messages is no sign of 12sec and more, I would rather argue that 9 sec happens between pressing power und the wake up process, where the kernel cannot log anything. S3/Deep is firmware assisted suspend.
If this delay does not occur with Windows with S3, then UEFI will probably react differently when using Windows. You can also pretend to be running Windows under Linux. Look here:
Anyway, what the firmware does in between is not open. Probably it does a warm up or something in that direction? I saw also laptops numerous times with wifi/bt cards which needs a bit more time to wake up, and sometimes it boot/wake up fast and then the card doesn’t get recognized → timeout. Probably that adds up here? But then Windows would have that problem also, but well probably not, because Windows handles drivers differently. Are you sure Windows uses S3 and not S0 suspend?