Most EMT-B programs that I've heard of generally require about 120 hours of classroom time and about 40 hours (approximately) of "clinical" time split between (usually) the ER and ambulance ride time (majority of the time). Although the training can be done in a matter of about 3-4 weeks, it is FAR less stressful for everyone if it's spread out over 3-4 months (Quarter-Semester length). I would be tickled pink if an EMT-B program had clinical time that went way beyond what's required!
As to the actual schedule, you should consult with someone at the program about the proposed schedule and check it against your work schedule. If you can make it fit, great! You'll also find that while some skills do carry over from CNA, much of it won't as you'll be learning a different skillset for a different job.