See if he can get a ressie and tix. For a one day just go thru the Disney app, which makes it really easy. I did a one day visit in November when I tagged along with my husband for a work trip and had a blast. Have him download the
Disneyland app and if he can play around with it today to familiarize himself with it it could help.
I did
genie+ because I figured I could do more in my one day and it worked great. A few good threads on how it works here. If he has time, mammoth club (Molly who used to be on allears) has some great DL content on YouTube that makes for a very accessible walk thru.