When I have two meetings: one at 1pm and the other at 3pm, which one is more appropriate?
- I have (two) meetings at 1pm and 3pm.
- I have a meeting at 1pm and 3pm.
Both can be said but to avoid the ambiguity, you need to have a pause while telling the first sentence. Or in writing, you may add a 'dash'.
I have (two) meetings (pause) --at 1 pm and at 3 pm.
With no pause, it MAY convey the message that you have two meetings at 1 pm and two meetings at 3 pm.
I can think of an another example in similar context -
I have two cars at home and (at) office
This, to my ears, brings in an ambiguity of having four cars.
I have two cars (pause) --at home and at office OR I have a car at home and another at office.
will mean two cars in total -one at office and one at home.
[However, it's quite obviously understood that one cannot have two meetings at the same time but above, I talked about English and not intellect!]
Also consider StoryMasterQ's opinion. It's straight and good (+1).
Your second option is also fine as it talks about one meeting at 1 pm and one more meeting at 3 pm.