Changed sleep() to send int64 in start_timer()

On my 32-bit system I was getting 
```ERROR: no method start_timer(TimeoutAsyncWork,Int32,Int32)```
when using ```sleep()```. Changed call to start_timer to use int64s
Merge pull request #2662 from amitmurthy/patch-1

Changed sleep() to call start_timer() with int64s