Is there any plugins that allow server events to only spawn at specific in game times?

TimedExecute allows for both in-game time and real time events.

I was looking at that plugin to do it, but would the normal events need to be disabled so they don't spawn other than that specific time?

Usually, yes. However, as per your other thread the cargoship event can't be controlled like that unfortunately.

Merged post

Caveat: it can't be done with a console commands anyway. I just know some clever-clogs will come along and make a mod for it ;)