Monks can got to bed any time that they want. They're all adults, and its an abbey, not a prison. Even the monks accused of sexual misconduct. They supposedly are required to have another monk to be with them at all times outside of the abbey, but we know this doesn't always happen.
Monks were investigated. SCSO has made several statements that multiple monks and priests were interviewed (not immediately after Josh went missing. Sadly, much later). We even have a statement from Fr. Wollmering that in 2006, Detective Soyka conducted a taped interview with him earlier that year.
People were and are being interviewed, but since the case is still unsolved, LE cannot reveal any progress on the case. It's happening, but that info is not always available to the public.