From the official site for the family:
Mom woke up before everyone else, got ready for work and left around 6:30am. Dad woke up shortly after and went to wake the children. It was around 8am when he noticed Isa was not in her room.
This was on the left under "Circumstances." Is this an error or is the time going to change now?
http://bringisahome.com/audio-sergio-celis-jr-and-rebecca-celis-911-call/
I see this a little different. I think it is fairly accurate on when Rebecca left for work.
This states that Sergio got up after Rebecca left. The rest is worded weirdly - how could he get up shortly after and wake up the children but not notice Isa was gone till 1.5 hours later? I don't think Sergio got up till quite a while after she left or else he got up and did stuff leaving the kids sleep till they needed to get up (this doesn't seem abnormal).
This sounds like Rebecca's version of the timing (relayed to someone who put it on the website) because when she left Sergio was still asleep or at least still lying in bed or on the couch. So Sergio would probably not have known if Rebecca had or hadn't checked on Isa before she went to work.