I read the Metro (free UK newspaper) way too much and for most celebrities it seems that they go away for a weekend and then they're "cured". I think for most of them it's a bit of a publicity stunt, but it's fair to say that for Richie it's something else.

I would have thought that the time in rehab is completely dependent on what doctors, the individual and what family/friends/employers (!) think.

I think it's fair to say though that if it's real "rehab" then it's more than just a weekend break. Rehab is over-used as a term as for most it seems to signify talking to a psychiatrist and getting out of the public eye for a little while. If you've got a serious problem (more than just psychological) then I would have thought the recovery period is anywhere from 0 > never.