Depends on time of day. An early morning (before 10 am) connection is less risky that a connection around 5 pm. I have comfortably made a number of 35 minute connections in the morning.

If you're connecting to the last flight of the day they are more likely to hold it if you're running a few minutes late. If you're on an earlier flight there is no chance they will hold the plane (or even hold your seat past T-15 minutes).

Also, if you're asking today about a connection next March, your question is pretty irrelevant. There is an almost 100% chance that there will be a schedule change between now and then that will make your connection different than 40 minutes.