I apologize if this has been covered before but I was hoping someone might be able to answer this for me. I'm checking on flights in July and August departing at a specific time and the only fares that are coming up on Delta are M and higher. I checked on Expertflyer and it shows that the other fare buckets have 0 availabilty even though the plane is empty.

F9 P9 A1 Y9 B9 M8 H0 Q0 K0 L0 U0 T0 E0

I've looked at several dates and every one for the specific time I'm looking at is the same. Is there a specific time when Delta loads the other fare buckets? Note: If I look at other departure times there are plenty of lower class fares available. When I check the seat map on Delta for the flight I'm looking at, it doesn't look like any seats are sold yet.

Just curious if there was a specific reason as to why one specific time of day wouldn't have any lower fares than M. BTW - The flight I'm looking at is DTW - SLC leaving at 8:30 am and it doesn't appear to matter what day I depart on in July or August.

Thanks in advance!