Here's a short list of some key dates and deadlines that you might want to add to your calendar.
This list isn't complete or guaranteed to be update to date and typo-free—it's just an informal heads up. Always check the academic calendar or communications from your college, Undergraduate Advising, Summer Orientation, etc. for official information about events and deadlines that matter to you!
Wednesday-Monday, February 21–26: Advising week for Spring 2018
Monday, February 26: Start of priority enrollment for Spring 2018. For more information, see the Schedule of Classes.
Monday, April 2: Spring quarter begins
Friday, April 20: Add/drop/swap and grade option deadlines
Monday, April 23: Add by petition begins