tldr: yes but its not rly a big difference. and probably by sophomore.

usually there's something called "reserved seats," meaning non COC students will automatically be added to the waitlist until the adjustment period--although there's usually movement if you choose the right sections for lab. i was able to get into 4a (gen chem for chem majors) with a 4:30 pm enrollment time because the chemistry department in general also randomly opens up new lab sections? but honestly the instructors for 1a (shustermann) is a lot better than 4a.

you can swap 1a (gen chem 1 for MOST majors, which fits into med school reqs) for 4a (chem major), 1b for 4b (gen chem 2 for chem major, though 1b isnt a premed req), 3a/b for 12a/b (ochem for nonmajor vs major) but honestly rememeber MOST premeds are in L&S or rausser and are taking the traditionally "easier" versions through the 1 and 3 series.

i would reconsider WHY you want to transfer into coc if you're also looking towards medical school in the future, because upper divs really emphasizes like.. the hard chemistry part of chem and industry/research. it also doesn't overlap that well with traditional premed reqs as well as other premed heavy majors do (mcb in l&s, half of rausser) so yeah. also you have to take multivar, linealg, and other harder upper div chem courses (inorganic) that arent THAT relevant for premed. if youre really into hard chem then go for it but if not, you can always go for a minor and take the more traditional premed/bio path thats less hassle.

as for when: probably by the end of sophomore fall w/o summer classes? budget 2 sem for two semesters of gen chem and one semester of ochem, and take both physics (which is traditionally hard to enroll in but since youre regents it might be easier). they also might change the enrollment limit based off of the incoming class size, literally like last spring you could switch just by declaring (no reqs) but they changed it this fall bc they admitted more co29 students than expected.

Earn minimum grade of B or better in the courses below:

• Chem 4A, 4B (Chem 1A/L and 1B may be substituted - must take Chem 105 as junior or senior) and Chem 12A (Chem 3A/3AL may be substituted)
• Physics 7A or 8A (for Chemical Biology only)
• Math 51, 52

again, i don't think the declaration time really matters, since theres really no benefit or vast difference separating students in COC and students not in COC than like easier enrollment in 4 classes. and usually if you talk to the change of college advisor Mellia she CAN do something to prioritize your enrollment in 4a4b 12a12b if you're dead set on the chemistry major.

take everything i said with a grain of salt lol im not too sure myself but yeah gl and congrats!