Strange behaviour with sleep() in a thread

I have a thread created with Thread.new that does some polling. I don’t
want it to busy wait so I call the sleep method like so:

sleep(60)

...this should allow me to poll every minute which is good enough 

for my
application. However, I’m finding that calling sleep from a thread in
this
manner often sleeps for a good deal longer than a minute. So far, I
find it
sleeping for about 8 or so minutes. The main thread is blocked in a
gets
call.
What I’m actually trying to do is implement a simple timer. I’m
trying
to do something at a certain point in time, like a cron job, without
busy
waiting.
Why is sleep behaving so strangely? Is there a simple way of doing
what
I’m trying to do?
Thank you…

Why is sleep behaving so strangely?  Is there a simple way of doing 

what
If you’re on 1.8.x then your two threads are actually one “real thread”
running two green threads. One of the green threads [the gets] might be
blocking and not allowing control to return to the other.
Fix (should this be the case): make the one not block, or use 1.9
Cheers!
-=r