Final answer:
Use the 'Hour of Day' AdWords report to analyze and optimize your bidding strategy for different times of the day to improve conversions.
Step-by-step explanation:
To investigate when you should modify your bidding during certain hours of the day to optimize conversions on AdWords, you should use the Hour of Day report. This report provides insights into how your ads perform at different times throughout the day. By analyzing this data, you can adjust your bids to target times when conversions are higher and avoid times when conversions are low. For example, if you see that your ads perform best between 5 PM and 9 PM, you might increase your bids during these hours to maximize visibility and conversions. Conversely, if performance dips in the early morning, you might lower your bids or pause bidding during that time.