Turn on timestamps by following these steps:
1) Select the gear icon in the top right hand corner of the 'Diary' tab
2) Choose 'Diary Settings'
3) Check the box next to 'Show time of day in Diary'.
Now when you add foods, biometrics, exercise or notes to your diary, there will be a 'Time of day' box that you can tick to add times to your entries. You can click directly on the time to change it to another time.