In case you missed it in tomorrow's the 23rd!
thread, BMW NA has provided this update on ordering guides and start of ordering date:
Originally Posted by BMWNA_MGuy
Everyone please go easy on your dealers
They don't have the order guide yet because I've been waiting on some final figures. Should have the order guide out sometime tomorrow (Thursday), but please give us a few hours to get it distributed. The actual order bank (when your dealer can put you in our system) is planned to open first week of May. My recommendation is to look the order guide over this weekend.
So watch out for the the US M5 Ordering Bulletin here sometime tomorrow