Shannon, if he is not urinating then he should not wait even 8 hours.
The urine could back up into his kidneys causing potentially fatal kidney
damage or the bladder could rupture.  The most common cause of this is
ultimately from an adrenal growth, even if this is the first symptom
of it and we've had one in that position have adrenal surgery on an
emergency basis.  Both enlarged prostate and crystal problems in male
ferrets typically do trace back to adrenal problems and surgery is
usually curative.
 
Here is a compilation which has the information you need:
http://www.smartgroups.com/vault/ferrethealth/prostate.txt
 
It even includes useful medications and vet, Jerry Murray, either in the
compilation or later (in which case, use the FHL archives) even went into
some possible useful precautionary measures.
 
I apologize for not being as clear as i could be; I'm at the tail end of
a bout of influenza; know several eastern seaboard folks in more than one
state who have had it already this year.  Do NOT forget that ferrets can
catch influenza.  Even with precautions a ferret we have who is
immunosupressants got it but he's fine now; the rest escaped getting it
with precautions -- especially tons of hand washing -- used.
 
>I created the original Magic 8 Ferret.  Then our friend Melissa created
>a talking version that uses Macromedia Shockwave (it's a free download
>if you don't already have it).
>
>http://www.asktheferret.com/asktheferret.html
 
Talking ferret?  I'll give you Talking Ferret! :-)  Take a look:
 
We have a good sized room for the ferrets but they also get supervised
time elsewhere, so when Ashling became thirsty during such an out time
and let me know while we were in the bedroom, I grabbed a bottle of water
from the stand and filled my glass while she watched so that she could
drink from it.  Maybe a half hour later I heard things falling in the
kitchen.  Ashling was doing something Steve and I have never seen her
do -- knocking over water bottles (only the ones of the same design as
the one in the bedroom).  When I came in she stared at me then pointed
her nose toward her dry water dish.  Yes, she was very thirsty.  Hey,
she communicates!
[Posted in FML issue 3917]