Returns an observable sequence that produces a value after dueTime has elapsed and then after each period. Note for
relative time is supported.
dueTime(Date|Number): Absolute (specified as a Date object) or relative time (specified as an integer denoting milliseconds) at which to produce the first value.
[period|scheduler=Rx.Scheduler.timeout](Number|Scheduler): Period to produce subsequent values (specified as an integer denoting milliseconds), or the scheduler to run the timer on. If not specified, the resulting timer is not recurring.
Scheduler): Scheduler to run the timer on. If not specified, the timeout scheduler is used.
Observable): An observable sequence that produces a value after due time has elapsed and then each period.