You check your BG to get information, what information do you want?
Depends. 1 hour or 2 hours .
Typical testing times are fasting, before eating, 1.5 - 2 hours after eating, and bedtime.
7.8 gives you an average blood sugar of close to 200.
The post eating numbers should guide you on adjusting your meals. Typically most people find that eating low carb meals will help in lowering blood sugars.
Are you on insulin? IF you are, then it is also important to check before meals to see if you are back to normal numbers, or too low, or too high before you ate.
You may also use blood sugar results to gauge the effects / benefits of exercise on your blood sugar levels.