I need to book a train for the morning of Saturday, March 14th from Marrakesh to Rabat. On the ONCF website the schedule lists hourly trains on the :35, starting in the early morning. But when I go to book, it shows the earliest train is 11:35am. When I look at some of the booking sites like 12go, they list the earlier trains and it appears you can book a reservation (not clear if it's actual ticket). We want to book a 9:35am train and prefer to book it on the ONCF site, but it's not there. Should I wait a while longer hoping he earlier trains will show up, or book using one of the booking sites (which one is recommended?). There will be 9 of us on this train.

I have also read many less than favorable reviews of ONCF. Might it make more sense to hire a van/mini-bus to drive us instead of the train?

This is our first time in Morocco, and starting in Rabat we will have a private guide through Morocco Countryside Tours. We arrive in Marrakech on the 13th.

It’s been a while but I enjoyed the train ride from Marrakech. I suggest, if the websites don’t do the job, go to the station when you arrive in the city and buy your tickets from a human at the ticket counter.

I found the trains in Morocco quite comfortable, though I didn't take one from Marrakesh to Rabat.

According to the Man in Seat 61, purchasing from 12go is a reasonable option:
https://www.seat61.com/train-travel-in-morocco.htm

I ended up contacting our guide, and they are providing the transportation, with a stop for lunch and to see the Mosque in Casablanca. Time and price similar for our group.

I know there's been terrible rain and flooding in the north there. After Rabat we go to Chefchaouen. Right now I'm reading the main road is damaged by the weather. Hopefully not too serious and it will be repaired by mid-March.

Are you committed to Chefchaouen? I skipped it after hearing that it's become a bit shoddy and overrun by tourists ... and there is so very much else to see and experience in Morocco!

Pretty much committed. I really wanted to see the "blue city". I dabble with photography and it looks very photogenic. Only spendng a night there then going to Fes.

There's a "blue city" section of Rabat. Essaouira, too.