srfi-18 in Racket

For some strange reason it doesn't seem to implement thread-sleep!. Is there a reason for this, and is there a more portable way to get a Scheme program to sleep for a specific amount of time?

Racket isn't a Scheme anymore in any real sense anymore as far as I'm concerned, they've changed the name for a reason. I'm porting my Racket code to a "practical" superset of R5RS to run eventually at least in Chicken and aiming for a R7RS-big app when that will happen, and I have to say the process isn't easy...

What does this do?
#lang r5rs
(#%require (lib "srfi/1")) ; SRFI-1

(display (delete-duplicates '(1 2 3 3 4)))
Answer:
[spoiler]Error: "null-list?: argument out of domain {1 2 3 3 4}" because '(1 2 3 4 5) is made out of some kind of [b]mcons[b] chain instead of cons.

The solution: substitute "srfi/1" with "srfi/%3a1" (wat...), which prints the expected (1 2 3 4).
[/spoiler]