You mentioned the mud crusts over before you finish a seam. What specific type of mud are you using, like all-purpose or a setting compound? Have you tried mixing in a commercial retarder instead of home remedies, since they're made for this exact problem? Also, how's the ventilation in that basement - can you get a fan blowing to move the damp air around?

Oh man, spacing out glue ups is the only way to go (seriously, it saves so many headaches). Piper's totally right about warping, because if you glue a panel into a frame that's still wet, the wood can't move as it dries and just fights itself. Giving each part time to fully dry and do its initial shrinking means everything settles before you lock it in place. Rushing that process is pretty much asking for a cracked panel or a pulled apart joint later on.