Looks like the first ferry to Cozumel is 6:30. Assuming you wanted to be up at the butt crack of dawn on vacation to get to the ferry pier in time, you could probably catch any dive op that leaves at 8. I have not dove with Christi (yet) but have no reservation recommending Blue XTSea as one of the top dive ops on the island. If your schedule will work or you can find extra divers, you won't be disappointed.
We dive Aldora for the steel 120 tanks and they will run a late afternoon dive with one being a twilight dive, the other being a night dove. Those have to be booked in advance though and may be dependent on a minimum number of divers. I believe they do guaranteed night dives on certain nights as well, but check with them. Aldora leaves their downtown pier about a block away from the ferry pier at 7:30(ish....it's Mexico). In theory....you could catch the Aldora boat if you did the paperwork in advance by email. The ferry usually takes around 45 minutes and you would want to be one of the first off and have your bag with you. Time for rental equipment might be tight for sizing issues, But if you only needed tanks and weights, it would be easy. We have waited 10-15 minutes for late divers many times before at the doc...never though twice about it.
I have dove with Blue Magic and they left their shop at 8ish. They paid for the taxi to get to the boat. Their shop is a few blocks from the ferry pier so that might work as well. Great shop and they have aluminum 100s available as an option too if you wanted to extend your dive times. (I like big tanks) Blue Magic felt like diving with family.
Tres Pelicanos has a large following here, and their shop is downtown, but I don't know what their schedule is or how you get to the boat. They have lots of fans on here for a reason.
My experience with the dive ops we have dove with in Coz is that the operators will do almost anything to accommodate a reasonable request. A 15 minute wait to depart won't ruin anyone's dive if needed. The key would be good communication and maybe a text or call once you were on the ferry to verify you were on the way.
Send the dive op of your choice an email with your needs and I'm sure you find something that works. We have around 80 dives in Cozumel and have never had a bad experience....even the less than perfect dives were great!!
Good luck, safe travels!
Jay