Associating times of day with meals
question 1 :

approximate time:

   早上 -- 6:00--8:00

   上午 -- 8:00 -- 12:00

   中午 -- 12:00 --14:00

   下午 -- 14:00 -- 18:00

   晚上 -- after 18:00


this my understanding(not formally), and splitted most by work time, i would say most people would agree

question 2:

there are three meals in Chinese(as in the saying : 一日三餐):

    早餐(breakfast) -- 早上 

    午饭（lunch）--- 中午

    晚饭（dinner）  -- 晚上 


question 3:

late breakfast -- there is no such thing（is there a name for it in English?）

brunch --  no such thing 

late lunch -- no such thing（is there a name for it in English?）


we Chinese kind of think this things unnormal, you should be woking during this time (8:00--12:00,14:00--18:00), and if you are eating there must be something wrong with your lifestyle, and we believe it is not good for your health, you should eat regularly.