Upvote:3
To answer my own question, buses from Boquete to David and from David to Panama City maintain the usual daily timetable throughout the carnival, and it was not a problem to buy a ticket on the day. In fact, tickets can only be bought on the day of travel. The early morning local bus from Boquete to David was somewhat crowded with a few people standing in the aisle. The long-distance bus from David to Panama City has assigned seats so even though most seats were occupied, it did not feel overly crowded.