Perform feature engineering for time series data with two fields: time and price. The data has irregular frequency, but is significantly higher than 1 second. At the end of each second, you need to look back at the last 5 minutes of data and calculate the variance of prices. Please use Python pandas to implement this feature engineering. Provide your response in exactly 2 paragraphs (separated nearby paragraphs with 3 aterisk symbols ***).
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