[Grammar] Omission of prepositions

[supergenie]

Hi,

I know that there are rules for omission of prepositions of time before "next, last, this" etc, are there any other circumstances that prepositions of time and location are omitted? I have noticed that prepositions are omitted sometimes before dates, for instance, I found both usages on the Internet as shown below. Are they both correct?

The deadline is 1 Jan.
The deadline is on 1 Jan.

There are 2 sentences in particular that I would like to seek your help. Which sentence is correct?

1. The venue is Ballroom 1 of H Hotel./ The venue is in Ballroom 1 of H Hotel.
2. The time is 6pm./ The time is at 6pm.

Thanks a lot!:-D

 

[Tdol]

1 I would not use a preposition, because the whole room is the venue.
2 I would not use a preposition because it is the time. I would say the meeting is at 6pm, not [strike]the time is at 6pm[/strike].