i just noticed the slow boot today, i know everything was working perfectly yesterday. before i went to bed i installed adobe premiere, photoshop, illustrator, after effects.
i booted this afternoon, it's taking maybe 2 minutes vs 30 seconds yesterday.
I have the same motherboard as you and ran into that issue as well.
You'll need to convert all your drives which I'm assuming are MBR (Master Boot Record) to GPT (GUID Partition Map).
To fix this you'll need to reformat your windows os drive(s) and install Windows via UEFI mode with the GPT...