I've been confused by this and also the chat at 3:45 with his friends saying he'd be late for the movie (since according to his story he didn't yet know Cooper was in the car, and he had plenty of time to get to the movie if he truly hadn't remembered), and something just hit me. This is speculation but it pulls the confusion together in my mind.
3:16 - RH texts LH asking when she's going to pick up his "buddy". This is according to defense. The police said he didn't see a text but it could have been deleted or sent through another system and they are still going through all that. IMO that text was a signal for her to go to the daycare and he would leave work.
When he hadn't heard back from her by 3:45 he realizes they are behind their planned schedule and he would be late for the movie so he chats with his buddies and tells them he'll be late.
JH's phone records show 4 missed calls from LH, they play phone tag and finally connect for a 1 minute call at 4:04. I am speculating that was the response he was waiting for to tell him to leave work because within 10 minutes of that call he leaves.
JMO