Covid - 88% saturation - post treatment.

Doctors, Hello! My FIL, male 63, was admitted in Oxygen Bed on May 1st with saturation of 88%, he was tested positive for Covid-19 and is being treated in the hospital. As of yesterday he was on 15L of oxygen and had a saturation of about 95, however today the saturation is at 88 without oxygen support. The hospital advices discharge as he was physically good and active in 2 days. So my question would be, 1. Should we be concerned? Is this abnormal? Is it dangerous? 1. Would 2 days be sufficient time to be discharged? 1. If discharged, how much of a risk would he be in? Is 88% fatal or dangerous? Or this is a normal pattern observed in recovering patients? Thanks Saravanan Prasadh