I usually have my patients wait 6 weeks before sleeping without a bra, but you should call your surgeon and follow his/her instructions.
Bra less at 5 weeks after reduction
It should be possible to go braless at five weeks after a breast reduction, but you should really follow your surgeon's instructions.
Bras after Breast Reduction
Surgeon recommendations vary regarding routine post op care. At 5 weeks, surgical incisions have 80% of normal tissue strength so are well healed. Sometimes wearing bras for longer periods of time is required for would healing issues. Most patients could go braless at this point, but would clear specifics with your surgeon as patients, situations, and surgeon preferences are all different.