if sentanced to in patient rehab do you wait for bed at detention federal detention center

There are no federal sentences that force an inmate into drug rehabilitation. Your inmate was NOT sentenced in federal court to do RDAP, if they get it it's great, but it's not a part of the sentence at all. It could be a recommendation but the Federal Bureau of Prisons makes all the decisions, the judge has nothing to do with it once they are property of the BOP.

RDAP is voluntary, but if eligible, it is the only way to carve a year off your sentence without snitching.