You may prescribe daily diary for each of the agents to be submitted to you the next morning for review. But, mind it that may also affect the performance efficiency of the agent in noting down particulars of each task in the diary. So, you can prescribe the diary to contain major achievements, including time taken for each such activity. You may also have to use some device or software, like call tracker, which can indicate the summary of total calls attended by each agent in a day.