Here is the relevant excerpt from Teslas employee stock purchase program:
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The employee stock purchase program is divided into six month time periods with two purchase dates: Feb 26th and Aug 31st.
First period is Sept 1 - Feb 26th
Second period is March 1st - Aug 31st
What is interesting is how Tesla determines the price for the shares.
Tesla looks at the closing price on the first and last trading days of the period. For the Feb purchase this could be Sept 1 and Feb 26th assuming both days are trading days.
Tesla then takes the lower of the two closing prices, applies a 15% discount on the lower price, and applies this share price as the purchase price for employees.
So the important dates are Sept 1st and Feb 26th, and also March 1st and Aug 31st. Since the dates are adjoining at the beginning and end of each period we can just focus on the purchase dates: Feb 26th and Aug 31st.