I want one word that means Date and Time. For example in "the date and time of the event will be announced later" I want to use single word instead of "date and time"
Just saying "date" should be sufficient:
In this usage, "date" implies time as well -- if the organizer of the event hasn't even determined the particular date yet, the exact time of day is probably up in the air as well. Another example: when you agree on a date and time to meet someone or do something with someone, you're often said to "make a date" or "have a date," and it's understood that that means the time as well as the day.
Similarly, "time" can imply date, as in:
In that sense, the speaker is referring to something that happened on a particular date and time, but the specific date and time are less important than the thing that happened.
On the other hand, sometimes you want to identify a particular instant that something happened. For that case, "moment" is a good word, as is the phrase "point in time":