My recent OS flights have opened checkin at t-47. I don't recall how it was when I last checked in with LH but it was more than 24h in advance. Either 36 or 47.
PRE means preboarding. Exit rows are now eligible for preboarding, did you perhaps get ASR on exits?
You should be able to add your M/M number if not present, but if your BP says LH*S on it, that is equivalent code to FTL.