I have read over the last two months several art teachers that seem to be in the same boat that you are in. The transition to a 45 to 55 min period from a 80 min period.
I have for years worked with a 55 min schedule. I see students everyday for 18 weeks. Our elective art classes run for a semester each. The key is to keep demo's or lectures to around 10 mins, have materials laid out and organized so students can pick them up, keep the traffic paths in class open so students can move about getting materials with ease, review clean up and figure depending on mediums a good 10 mins for the most messy. Under this schedule work gets stretched out more and flow of ideas sometimes is hampered because a student just gets started then has to stop and clean up.
If you think it will be hard getting use to think about how it will be for students who are use to the 80 min classes. On the first day talk about that and let them know you all have to work as a team to make it work. Respect of materials and being responsible for ones on clean up is "very" important now with the limited time frame.
Question: Why did they change the schedule? No one has really answered that. I am curious.