Observable with timer will delay the publishing the event to the the time specified. It can be used if you want the Observable to delay the publishing of source events for some time.
It will publish a Single element after the time specified.

Below logs will show that event is published after specified time of 5 seconds.

23-01-20 13:29:49 [main] [INFO ] [c.c.l.rxjava.observers.DemoObserver]- onSubscribe
23-01-20 13:29:54 [RxComputationThreadPool-1] [INFO ] [c.c.l.rxjava.observers.DemoObserver]- onNext -> 0
23-01-20 13:29:54 [RxComputationThreadPool-1] [INFO ] [c.c.l.rxjava.observers.DemoObserver]- onComplete