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:
The date of the event will be announced later.
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:
I remember the time we went camping and Dad swallowed a bug!
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":
The world changed the moment Armstrong set foot on the moon.
In technical writing where precision is necessary, the term datetime has been coined when it is necessary to be precise that date and time are to be specified. This is particularly common in documentation of computer systems and databases.
I have never, however, seen this term used in a non-technical setting (that I can recall).