Observable.Timer TimeSpan.FromTicks(30) stop working after two executes.

Hello and thank you for using dotnet/reactive. Please select a category and detail your issue by answering the questions there:

#### Bug

Despite our best efforts, bugs can slip into releases or corner cases forgotten about. We will try our best to remedy the situation
and/or provide workarounds. Note that certain (odd) behaviors are by design and as such are not considered bugs.

> Which library version?
5.0.0
> What are the platform(s), environment(s) and related component version(s)?
Windows 10 20H2 19042.867, with .net 5.0
> What is the use case or problem?
```
_recvObs = Observable.Timer(DateTimeOffset.Now.AddSeconds(5), TimeSpan.FromTicks(30));
_recvObs.Subscribe(RecvDataFunc);
```
> What is the expected outcome?
RecvDataFunc should working each 30 ticks
> What is the actual outcome?
RecvDataFunc works only twice (two times).
> What is the stacktrace of the exception(s) if any?
no exception
> Do you have a code snippet or project that reproduces the problem?
```
private IObservable _recvObs;
...
_recvObs = Observable.Timer(DateTimeOffset.Now.AddSeconds(5), TimeSpan.FromTicks(30));
_recvObs.Subscribe(RecvDataFunc);
...
private void RecvDataFunc(long i)
```

I've used the Thread to maintain TCP connections, as I saw reactive would be better easily doing the timer/task, and I simply replace the Thread with Observable as code shows above.
it works with TimeSpan.FromSeconds which inv large than 1 second, and zero value, but FromTicks(30).
It seems a bug for me, I've switched back to Thread.