My observation has been that a few EUA seats are released to Plat at the 5 day EUA (you can check the seat maps after 9pm) and likely only to the point of the higher fare codes. Afterwards I have not seen any EUA's at all, even though there may be 8 of out 12 FC seats still available.

Prior to March 16th, it would be possible for a silver to check in (I have seen it first hand) and get an OLCI up, even though a Plat did not get EUA'ed the night before. The OLCI had to occur in the afternoon, not 24 hours before.

Now after March 16th, it appears the OLCI up has gone away. All seats are held and processed at the gate. On a flight IAH-SNA a few week ago (after 3/16), Galileo showed A7 - six hours before departure. Then at the gate, it looks like 7 people were called up for new F boarding passes. The agents had a list of the sorted elite ups.