Is that right?
1. I usually eat dinner in 5pm.
2. It is 3pm in beijing, China.

Question

Answer

I usually eat dinner AT 5pm.
We use preposition AT for time ( e.g. at 4:30, at 19 o'clock)
Preposition ON is used when we speak about days of the week (on Monday)
And preposition IN is used for seasons ( in Spring), years ( in 1956)
I hope this helps.

Answer

IN use it with >> Months or Seasons ( e.g. in May or in Winter)

ON use it with >> days of week (e.g. On Saturday elc)

AT use it with >> describe time ( at 9 o'clock )

So , you should use here AT not IN

Answer

1) I usually eat dinner at 5pm
  'at' in this sentance normally means you start eating dinner when it becomes 5pm - if you used 'in' you would be taking about the time it takes to eat dinner. Example: I noramlly eat dinner in 5 minutes.

2) It is 3pm in Beijing, China. 
This sentance is perfectly fine.