If you use bone standard JEDEC, your POST time will be shorter, but still not as short as on a non-AM5 system. What matters is your memory configuration in general. You'll POST quicker with 2 sticks of single rank memory than with 4 sticks, or dual rank.
Or maybe you just don't notice it because you're used to it like I am.
Seriously, whether I see the POST screen 5 seconds, or 25 seconds after I press the power button is kind of a "first world problem", imo. If this is one's biggest concern in life, then one is very lucky.