Typically the EventScheduler holds the time and has some methods for scheduling events (e.g. scheduleNow, scheduleDelayed, scheduleAbsolute) as well as canceling events (cancel). Often the EventScheduler also holds the time. Thus the interface roughly looks as follows:

{{{
#!cplusplus
class EventScheduler
{
    void
    scheduleNow(Event);

    void
    scheduleDelayed(SimTime, Event);

    void
    scheduleAbsolute(SimTime, Event);

    void
    cancel(Event);

    SimTime
    now();
}
}}}

However, the time need not be part of the EventScheduler. See the EventScheduler in Python sched.scheduler for a nice idea.