The common - but not entirely evidence based - believe is that 500 milers go
onto the PA once their window arrives.
If you are a 1K that would mean that between -100 hours to scheduled depature
and -24 hours to it, they would beat miles to ug chances.

However if inventory management releases seats more than 100 hours (or shorter,
depending on your status) out, your 500 milers would not kick in at all.
This is why miles are regarded a confirmed instrument.

If clearing the ug is your only concern in life then you should either a) leave
the ug waitlisted on miles until right before your window and then switch to
500er certs or b) trade the miles for a CR1 on the Coupon Connection and
be on the PA all the way...