Hmm, could it be the temperature climbs during the night as your air-con is shut after office hour?
I had a planted tank in office previously with similar situation - livestocks were stressed in the morning and looks better in the afternoon and cycle repeat. In the end, I found out one day when I have to got back office at 2am, the temperature was 32 degrees before air-con is on!
I finally address the problem by installing a fan to come on after the central air-con is off. Hope that helps.